Information reproducing method judging a multivalued level of a present cell by referring to judged multivalued levels of a preceding cell and an ensuing cell

ABSTRACT

A mark representing information of a multivalued level is recorded in each of cells arranged in a recording medium. Upon reproducing the multivalued level from a reproduction signal of the recording medium, the multivalued level of a present cell is judged by referring to a judged multivalued level of a preceding cell preceding the present cell or an ensuing cell ensuing the present cell, or by referring to the judged multivalued levels of both the preceding cell and the ensuing cell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an information recordingmethod, an information recording device, an information reproducingmethod, an information reproducing device, an informationrecording/reproducing device, and a recording medium, and moreparticularly, to an information recording method, an informationrecording device, an information reproducing method, an informationreproducing device, an information recording/reproducing device, and arecording medium which deal with data having a mark representinginformation of a multivalued level recorded on a cell.

2. Description of the Related Art

Conventionally, in an optical disc, binary digital data is recorded on aspiral or concentric track, in such forms as uneven pits formed byembossing, etc. (on a ROM disc), holes formed in an inorganic/organicrecording film (on a recordable (write-once) disc), differences betweencrystal conditions (on a phase change disc), or differences betweenmagnetization directions (on a magneto-optical disc). Upon reproducingthese recorded data, a laser beam is projected on the track, anddifferences in intensities of reflected lights therefrom or differencesin polarization directions due to magnetic Kerr effects are detected soas to obtain a reproduction RF signal. Then, the obtained reproductionRF signal is processed according to a constant threshold value, forexample, so as to detect the binary data.

For the purpose of increasing a recording density of information, amethod of recording, not binary data, but ternary or furthermultivalued-level data, has been contrived; however, in an optical disc,a level fluctuation or an amplitude fluctuation occurs in a reproductionsignal due to various factors, such as differences in reflectance amongvarious types of optical discs, or differences in reproduction frequencycharacteristics between inner and outer tracks in one optical disc.Therefore, when a threshold value used in detecting multivalued-leveldata is constant, the reproduction signal is possibly detected at awrong value. Especially, since multivalued-level data, such asthree-valued or four-valued data, require a plurality of thresholdvalues, the multivalued-level data is more likely to be detectedincorrectly.

For the purpose of solving the above-described problems, JapaneseLaid-Open Patent Application No. 5-54391 discloses as follows. Areproduction signal reproduced from a recording medium on whichmultivalued-level data is recorded is subjected to an A/D conversionaccording to a reference clock, and a signal level data obtained by thisA/D conversion is compared with threshold values so as to detect themultivalued-level data; in this course, the signal level data obtainedfrom the reproduction signal by the above-mentioned A/D conversion isstored in a memory means on a predetermined signal unit basis, anddistribution information of the signal level data is obtained for eachof the predetermined signal units stored in the memory means; then, thisdistribution information determines threshold values used for detectingthe multivalued-level data from the signal level data in the presentsignal unit. Further, the above-mentioned course is based on a use of aformat in which a proportion of level values of recorded data is fixed.

For example, on a predetermined signal unit basis, such as areproduction signal in sector units in a recording format on an opticaldisc, a signal level data obtained from the reproduction signal by anA/D conversion is temporarily stored in a memory, and distributioninformation of occurrence frequencies thereof is obtained by using a CPUso as to obtain optimal threshold values as criteria for detectingmultivalued-level data; and multivalued-level data is redetected fromthe stored signal level data by using the threshold values. Therefore,even when a level fluctuation or an amplitude fluctuation occurs in thereproduction signal, the multivalued-level data is less likely to bedetected incorrectly so as to realize an accurate multi-value detection,which consequently promotes an increase in a recording density ofrecording data.

In Japanese Laid-Open Patent Application No. 5-54391, for the purpose ofdealing with a fluctuation in a long period, such as a signal levelfluctuation in inner and outer tracks of an optical disc, thresholdvalues used for detecting multivalued-level data are optimized on anindividual sector basis, for example. Additionally, a restriction isimposed on a format as a precondition so as to orderly separatemultivalued-levels which include variations.

By the way, increasing a recording density of information-necessitates,not only the use of multivalued data, but also a miniaturization of aunit of data recording/reproduction (hereinafter referred to as an“information cell” or simply a “cell”). When the information cell is sominiaturized that a plurality of information cells become encompassedwithin a reproduction light beam spot (see a description made later withreference to FIG. 1A to FIG. 1D), an output level of a reproductionsignal of the information cell comes under influences of preceding andensuing information cells such that output levels of reproductionsignals corresponding to a same multivalued level shift (vary) dependingon which multivalued level the preceding and ensuing information cellspossess, as a result of which a variation (an expansion) of each ofmulti-valued levels becomes larger, apparently. Therefore, when compiledin a long period, such as a sector unit, distributions of adjacentmulti-valued levels overlap one another. FIG. 2, details of which willbe described hereinafter, shows an actual example of a leveldistribution of reproduction signals in a case where a multi-valuedlevel (=eight-valued data level) is recorded in one information cell,and the reproduction light beam spot has a size encompassing threeinformation cells. In this example, distributions overlap between levels1 and 2, levels 2 and 3, and levels 4 and 5.

When applying a detecting method as disclosed in Japanese Laid-OpenPatent Application No. 5-54391 to such a reproduction signal asdescribed above, there is a problem that a level of an information cellis highly likely to be detected incorrectly due to the overlap ofdistributions, in whatever manner the threshold values are determined.Further, the restriction imposed on a degree of freedom regarding aformat is also a problem.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedand useful information recording method, an information recordingdevice, an information reproducing method, an information reproducingdevice, an information recording/reproducing device, and a recordingmedium in which the above-mentioned problems are eliminated.

A more specific object of the present invention is to provide aninformation recording method, an information recording device, aninformation reproducing method, an information reproducing device, aninformation recording/reproducing device, and a recording medium whichcan reduce a likelihood of erroneously judging a multivalued level uponreproducing a cell in which information of the multivalued level isrecorded, and furthermore, which can prevent influences of an erroneousjudgment of a multivalued level from being propagated to other cellseven when such an erroneous judgment occurs due to a defect and soforth.

Especially, an object of the present invention is to provide aninformation reproducing method, an information reproducing device, aninformation recording/reproducing device, and a recording medium whichcan prevent an erroneous judgment due to an inter-code interferencebetween a present cell being processed and each of preceding and ensuingcells.

Further, an object of the present invention is to provide an informationreproducing method, an information reproducing device, an informationrecording/reproducing device, and a recording medium which can performan excellent multivalued level judgment by effectively utilizing adegree of an inter-code interference between a present cell beingprocessed and each of preceding and ensuing cells.

In order to achieve the above-mentioned objects, there is providedaccording to one aspect of the present invention an informationrecording method for recording a mark representing information of amultivalued level on each of cells of an information recording medium,the method comprising the step of recording an M-valued mark on one cellin every predetermined number of cells so as to intervene between cellshaving N-valued marks, where N is an integer equal to or larger than 3,and M is an integer smaller than N.

According to the present invention, upon reproducing, at least a levelof the M-valued mark can be judged without error. Therefore, theinformation recording method according to the present invention improvesa reliability of reproducing multivalued information, compared to auniform recording with N-valued marks.

Additionally, in the information recording method according to thepresent invention, N may be 2^(T) representing T-bit data, and M may be2^(T−1) representing (T−1)-bit data having a lowest-order bit among theT-bit data fixed at one of 0 and 1.

According to the present invention, N is set at 8, and M is set at 4,for example, so that the M-valued mark assumes thinned out levelscompared to the N-valued mark, whereas the M-valued mark and theN-valued mark can be recorded according to a common marking system.Additionally, a level of the M-valued mark can be judged more correctly.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationreproducing method for reproducing a multivalued level from areproduction signal of a recording medium in which a mark representinginformation of the multivalued level is recorded on a cell, the methodcomprising, a judging step of judging a multivalued level of a presentcell by referring to a judged multivalued level of at least one, i.e.,both or either, of a preceding cell preceding the present cell and anensuing cell ensuing the present cell.

According to the present invention, even when an output level of areproduction signal is subjected to influences of marks recorded onpreceding and/or ensuing cells, a multivalued level of a present cellcan be judged with less probability of erroneous judgment by referringto judged multivalued levels of the preceding cell and/or the ensuingcell. This method involves no inconveniences, such as imposing arestriction on a format of the recording medium.

Additionally, the information reproducing method according to thepresent invention may comprise a re-judging step of selecting either ofthe judged multivalued levels of the preceding cell and the ensuing cellaccording to an amount of an inter-code interference from either of thepreceding cell and the ensuing cell to the reproduction signal of thepresent cell so as to re-judge the multivalued level of the present cellby referring to the selected judged multivalued level.

According to the present invention, influences imposed by marks ofpreceding and ensuing cells on a multivalued-level judgment of a presentcell are determined from magnitudes of inter-code interferences so as toswitch judged multivalued levels to be used in re-judging themultivalued level of the present cell. Therefore, even when areproduction signal is subjected to the influences of the marks recordedon the preceding and/or ensuing cells, the multivalued level of thepresent cell can be judged with less probability of erroneous judgment.

Additionally, the information reproducing method according to thepresent invention may comprise a step of determining the amount of theinter-code interference according to a result of a multivalued-leveljudgment performed by using a level of the reproduction signal derivingfrom each of the present cell, the preceding cell and the ensuing cell.

According to the present invention, amounts of inter-code interferencesimposed from marks of preceding and ensuing cells to a multivalued-leveljudgment of a present cell are determined beforehand according to aresult of a multivalued-level judgment performed by referring to thereproduction signal deriving from each of the cells. Therefore, a judgedmultivalued level to be referred to can be selected appropriately amongthe preceding cell and the ensuing cell so as to enhance a reliabilityof the multivalued-level judgment.

Additionally, in the information reproducing method according to thepresent invention, the re-judging step may re-judge the multivaluedlevel of the resent cell by referring to the judged multivalued level ofthe preceding cell when the amount of the inter-code interference fromthe preceding cell to the reproduction signal of the present cell islarger than the amount of the inter-code interference from the ensuingcell to the reproduction signal of the present cell.

According to the present invention, degrees of inter-code interferencesare used effectively so as to appropriately select the judgedmultivalued level of the preceding cell, enhancing a reliability of themultivalued-level judgment.

Additionally, in the information reproducing method according to thepresent invention, the re-judging step may re-judge the multivaluedlevel of the present cell by referring to the judged multivalued levelof the ensuing cell when the amount of the inter-code interference fromthe preceding cell to the reproduction signal of the present cell issmaller than the amount of the inter-code interference from the ensuingcell to the reproduction signal of the present cell.

According to the present invention, degrees of inter-code interferencesare used effectively so as to appropriately select the judgedmultivalued level of the ensuing cell, enhancing a reliability of themultivalued-level judgment.

Additionally, in the information reproducing method according to thepresent invention, the re-judging step may determine a judgedmultivalued level of the present cell to be either of Y1 and Y2, Y1being a judged multivalued level of the present cell re-judged byreferring to the judged multivalued level of the preceding cell, and Y2being a judged multivalued level of the present cell re-judged byreferring to the judged multivalued level of the ensuing cell, when theamount of the inter-code interference from the preceding cell to thereproduction signal of the present cell is substantially equal to theamount of the inter-code interference from the ensuing cell to thereproduction signal of the present cell, and the judged multivaluedlevels Y1 and Y2 coincide.

According to the present invention, degrees of inter-code interferencesare used effectively so as to appropriately perform themultivalued-level judgment when the amounts of the inter-codeinterferences are substantially equal.

Additionally, the information reproducing method according to thepresent invention may comprise a step of comparing magnitudes of |y−y1|and |y−y2|, y1 being a learned level value of the reproduction signalestimated from a judged multivalued level Y1 of the present cellre-judged by referring to the judged multivalued level of the precedingcell, y2 being a learned level value of the reproduction signalestimated from a judged multivalued level Y2 of the present cellre-judged by referring to the judged multivalued level of the ensuingcell, and y being an actually measured level value of the reproductionsignal of the present cell, in a case where the amount of the inter-codeinterference from the preceding cell to the reproduction signal of thepresent cell is substantially equal to the amount of the inter-codeinterference from the ensuing cell to the reproduction signal of thepresent cell, and the judged multivalued level Y1 and the judgedmultivalued level Y2 do not coincide, wherein the re-judging stepdetermines a judged multivalued level of the present cell to be thejudged multivalued level Y1 when |y−y1| is smaller than |y−y2|, anddetermines a judged multivalued level of the present cell to be thejudged multivalued level Y2 when |y−y1| is larger than |y−y2|.

According to the present invention, amounts of inter-code interferencesimposed from marks of preceding and ensuing cells to a judged level of amark of a present cell are determined by comparing errors between signalvalues estimated according to learned results and an actually measuredvalue. Therefore, even when results are vague in determining amounts ofthe inter-code interferences according to a judged value obtained byperforming a multivalued-level judgment based on the reproduction signalderiving from each of the cells, a multivalued level of the mark of thepresent cell can be judged appropriately so as to enhance a reliabilityof the multivalued-level judgment.

Additionally, the information reproducing method according to thepresent invention may comprise a step of determining the amount of theinter-code interference by comparing a learned level value y1 of thereproduction signal estimated from a judged multivalued level Y1 of thepresent cell re-judged by referring to the judged multivalued level ofthe preceding cell, a learned level value y2 of the reproduction signalestimated from a judged multivalued level Y2 of the present cellre-judged by referring to the judged multivalued level of the ensuingcell, and an actually measured level value y of the reproduction signalof the present cell, after performing a multivalued-level judgment byusing a level of the reproduction signal deriving from each of thepresent cell, the preceding cell and the ensuing cell.

According to the present invention, a result of comparing errors betweensignal values estimated according to learned results and an actuallymeasured value is used in determining amounts of inter-codeinterferences imposed from marks of preceding and ensuing cells to amultivalued-level judgment of a present cell. Therefore, a judgedmultivalued level to be referred to can be selected appropriately amongthe preceding cell and the ensuing cell so as to enhance a reliabilityof the multivalued-level judgment.

Additionally, in the information reproducing method according to thepresent invention, the re-judging step may determine a judgedmultivalued level of the present cell to be the judged multivalued levelY1 when |y−y1| is smaller than |y−y2|, and may determine a judgedmultivalued level of the present cell to be the judged multivalued levelY2 when |y−y1| is larger than y−y2|, according to a result of comparingmagnitudes of |y−y1| and |y−y2|.

According to the present invention, degrees of inter-code interferencesare used effectively so as to appropriately determine a judgedmultivalued level of a present cell, enhancing a reliability of themultivalued-level judgment.

Additionally, in the information reproducing method according to thepresent invention, a judged multivalued level of the present cell isused for judging multivalued levels of ensuing cells when the judgedmultivalued level of the present cell is rewritten.

According to the present invention, a result of re-judging a multivaluedlevel of a present cell is fed back to multivalued-level judgments ofensuing cells so as to increase a reliability of results of determiningamounts of inter-code interferences imposed from marks of preceding andensuing cells to a judged level of a mark of the present cell, enhancinga reliability of the multivalued-level judgments.

Additionally, the information reproducing method according to thepresent invention may comprise a reproducing step of reproducing learnedpattern information of known multivalued levels from the recordingmedium in which all combination patterns of a group of three marks arerecorded beforehand as the learned pattern information, and a creatingstep of creating at least one criterion table according to level-valueinformation of the reproduction signal obtained from the learned patterninformation, wherein the criterion table is used for judging themultivalued level of the present cell.

According to the present invention, a multivalued level of a presentcell is judged by using the criterion tables created according tolevel-value information of a reproduction signal obtained from thelearned pattern information; thereby, the above-described informationreproducing method according to the present invention can be realizedwith ease. Additionally, the criterion tables are created according toresults of statistical processing applied to the learned patterninformation of known multivalued levels reproduced from information areain which the learned pattern information is recorded beforehand.Thereby, disturbances, such as fluctuations in write/read optical powersand a distortion of a medium substrate, can be learned so as to createthe criterion tables enabling a correction of erroneous judgment due tothese disturbances.

Additionally, in the information reproducing method according to thepresent invention, the creating step may create a present-cell judgmenttable, a preceding-cell reference table and an ensuing-cell referencetable as the criterion tables.

According to the present invention, the present-cell judgment table, thepreceding-bell reference table and the ensuing-cell reference table areused as the criterion tables so as to appropriately determine factors,such as amounts of inter-code interferences, which consequently enhancesa reliability of the multivalued-level judgment.

Additionally, in the information reproducing method according to thepresent invention, the creating step may create the present-celljudgment table according to a process ignoring level values of thepreceding cell and the ensuing cell among the level-value information ofthe reproduction signal obtained from the learned pattern information,may create the preceding-cell reference table according to a processignoring a level value of the ensuing cell among the level-valueinformation of the reproduction signal obtained from the learned patterninformation, and may create the ensuing-cell reference table accordingto a process ignoring a level value of the preceding cell among thelevel-value information of the reproduction signal obtained from thelearned pattern information.

According to the present invention, the criterion tables can be createdaccording to as few processes as possible.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationreproducing method for reproducing a multivalued level from areproduction signal of an information recording medium in which a markrepresenting information of the multivalued level is recorded on each ofcells so that an M-valued mark is recorded on one cell in everypredetermined number of cells so as to intervene between cells havingN-valued marks, where N is an integer equal to or larger than 3, and Mis an integer smaller than N, the method comprising the step ofswitching numbers of multivalued judgment levels between N and M witheach predetermined number of the cells so as to judge a multivaluedlevel of a present cell having one of the N-valued mark and the M-valuedmark.

According to the present invention, upon reproducing, at least a levelof the M-valued mark can be judged without error.

Additionally, in the information reproducing method according to thepresent invention, the multivalued level of the present cell having theM-valued mark may be judged by switching the number of the multivaluedjudgment levels to M so that the multivalued level of the present cellis judged according to the reproduction signal of the present cellalone.

According to the present invention, the multivalued level of the presentcell having the M-valued mark that has a smaller number of levels thanthe N-valued mark can be determined uniformly according to thereproduction signal of the present cell alone.

Additionally, in the information reproducing method according to thepresent invention, the multivalued level of the present cell having theN-valued mark may be judged by switching the number of the multivaluedjudgment levels to N so that the multivalued level of the present cellis judged according to criteria determined by referring to a judgedmultivalued level of a preceding cell preceding the present cell.

According to the present invention, even when an output level of thereproduction signal of the present cell is subjected to an influence ofthe preceding cell, the multivalued level of the present cell can beprevented from being judged incorrectly. Additionally, as for theM-valued mark recorded on one cell in every predetermined number ofcells, a multivalued level of the cell having the M-valued mark can bejudged without error according to the reproduction signal of the cellalone. Therefore, a propagation of a level judgment error occurring dueto a defect and so forth can be stopped at each cell having the M-valuedmark so as to prevent successive reproduction errors.

Additionally, in the information reproducing method according to thepresent invention, the multivalued level of the present cell having theN-valued mark may be judged by switching the number of the multivaluedjudgment levels to N so that the multivalued level of the present cellis judged according to criteria determined by referring to a judgedmultivalued level of an ensuing cell ensuing the present cell.

According to the present invention, even when an output level of thereproduction signal of the present cell is subjected to an influence ofthe ensuing cell, the multivalued level of the present cell can beprevented from being judged incorrectly. Additionally, as for theM-valued mark recorded on one cell in every predetermined number ofcells, a multivalued level of the cell having the M-valued mark can bejudged without error according to the reproduction signal of the cellalone. Therefore, a propagation of a level judgment error occurring dueto a defect and so forth can be stopped at each cell having the M-valuedmark so as to prevent successive reproduction errors.

Additionally, in the information reproducing method according to thepresent invention, the multivalued level of the present cell having theN-valued mark may be judged by switching the number of the multivaluedjudgment levels to N so that the multivalued level of the present cellis judged according to criteria determined by referring to judgedmultivalued levels of a preceding cell preceding the present cell and anensuing cell ensuing the present cell.

According to the present invention, even when an output level of thereproduction signal of the present cell is subjected to influences ofthe preceding cell and the ensuing cell, the multivalued level of thepresent cell can be prevented from being judged incorrectly.Additionally, as for the M-valued mark recorded on one cell in everypredetermined number of cells, a multivalued level of the cell havingthe M-valued mark can be judged without error according to thereproduction signal of the cell alone. Therefore, a propagation of alevel judgment error occurring due to a defect and so forth can bestopped at each cell having the M-valued mark so as to preventsuccessive reproduction errors.

Additionally, in the information reproducing method according to thepresent invention, the multivalued level of the present cell having theN-valued mark may be judged by switching the number of the multivaluedjudgment levels to N so that the multivalued level of the present cellensuing a cell having the M-valued mark is judged according to criteriadetermined by referring to a judged multivalued level of the cell havingthe M-valued mark preceding the present cell, and that the multivaluedlevel of the present cell preceding a cell having the M-valued mark isjudged according to criteria determined by referring to a judgedmultivalued level of the cell having the M-valued mark ensuing thepresent cell, when the predetermined number of the cells is three.

According to the present invention, when the M-valued mark is recordedon one cell in every three cells, the present cell having the N-valuedmark is adjacent to either of the preceding cell having the M-valuedmark and the ensuing cell having the M-valued mark. Accordingly, themultivalued level of the present cell can be judged more appropriatelyby referring to a judged multivalued level of either of the precedingcell and the ensuing cell.

Additionally, in the information reproducing method according to thepresent invention, the multivalued level of the present cell having theN-valued mark may be judged by switching the number of the multivaluedjudgment levels to N so that the multivalued level of the present cellensuing a cell having the M-valued mark is judged according to criteriadetermined by referring to a judged multivalued level of the cell havingthe M-valued mark preceding the present cell, that the multivalued levelof the present cell preceding a cell having the M-valued mark is judgedaccording to criteria determined by referring to a judged multivaluedlevel of the cell having the M-valued mark ensuing the present cell, andthat the multivalued level of the present cell not adjacent to a cellhaving the M-valued mark is judged according to criteria determined byreferring to judged multivalued levels of a preceding cell preceding thepresent cell and an ensuing cell ensuing the present cell, when thepredetermined number of the cells is four.

According to the present invention, when the M-valued mark is recordedon one cell in every four cells, the present cell having the N-valuedmark is adjacent to either of the preceding cell having the M-valuedmark and the ensuing cell having the M-valued mark, or is adjacent toneither the preceding cell having the M-valued mark nor the ensuing cellhaving the M-valued mark. Accordingly, the multivalued level of thepresent cell adjacent to either of the preceding cell having theM-valued mark and the ensuing cell having the M-valued mark can bejudged more appropriately by referring to a judged multivalued level ofeither of the preceding cell and the ensuing cell; the multivalued levelof the intermediate cell adjacent to neither the preceding cell havingthe M-valued mark nor the ensuing cell having the M-valued mark can bejudged more appropriately by referring to judged multivalued levels of apreceding cell preceding the intermediate cell and an ensuing cellensuing the intermediate cell.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationreproducing device reproducing a multivalued level from a reproductionsignal of a recording medium in which a mark representing information ofthe multivalued level is recorded on a cell, the device comprising, anA/D converting unit converting the reproduction signal into digitaldata, a multivalued level data retaining unit retaining multivaluedlevel data of a preceding cell preceding a present cell, ajudging-criteria changing unit changing criteria for judging amultivalued level of the present cell according to individualmultivalued levels of the preceding cell, and an operation unitdetermining multivalued level data of the present cell according to thecriteria changed by the judging-criteria changing unit based on thedigital data converted by the A/D converting unit and the multivaluedlevel data of the preceding cell retained by the multivalued level dataretaining unit.

According to the present invention, even when an output level of areproduction signal is subjected to an influence of a mark recorded on apreceding cell, a multivalued level of a present cell can be judged withless probability of erroneous judgment by changing criteria for judgingthe multivalued level of the present cell according to a multivaluedlevel of the preceding cell.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationreproducing device reproducing a multivalued level from a reproductionsignal of a recording medium in which a mark representing information ofthe multivalued level is recorded on a cell, the device comprising anA/D converting unit converting the reproduction signal into digitaldata, a digital-data retaining unit retaining the digital data convertedby the A/D converting unit, an ensuing cell level operation unitdetermining multivalued level data of an ensuing cell ensuing a presentcell prior to determining multivalued level data of the present cell, ajudging-criteria changing unit changing criteria for judging amultivalued level of the present cell according to individualmultivalued levels of the ensuing cell, and an operation unitdetermining the multivalued level data of the present cell according tothe criteria changed by the judging-criteria changing unit based on thedigital data retained by the digital-data retaining unit and themultivalued level data of the ensuing cell determined by the ensuingcell level operation unit.

According to the present invention, even when an output level of areproduction signal is subjected to an influence of a mark recorded onan ensuing cell, a multivalued level of a present cell can be judgedwith less probability of erroneous judgment by changing criteria forjudging the multivalued level of the present cell according to amultivalued level of the ensuing cell.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationreproducing device reproducing a multivalued level from a reproductionsignal of a recording medium in which a mark representing information ofthe multivalued level is recorded on a cell, the device comprising, anA/D converting unit converting the reproduction signal into digitaldata, a digital-data retaining unit retaining the digital data convertedby the A/D converting unit, a multivalued level data retaining unitretaining multivalued level data of a preceding cell preceding a presentcell, an ensuing cell level operation unit determining multivalued leveldata of an ensuing cell ensuing the present cell prior to determiningmultivalued level data of the present cell, a judging-criteria changingunit changing criteria for judging a multivalued level of the presentcell according to individual multivalued levels of the preceding celland the ensuing cell, and an operation unit determining multivaluedlevel data of the present cell according to the criteria changed by thejudging-criteria changing unit based on the digital data retained by thedigital-data retaining unit, the multivalued level data of the precedingcell retained by the multivalued level data retaining unit, and themultivalued level data of the ensuing cell determined by the ensuingcell level operation unit.

According to the present invention, even when an output level of areproduction signal is subjected to influences of marks recorded onpreceding and ensuing cells, a multivalued level of a present cell canbe judged with less probability of erroneous judgment by changingcriteria for judging the multivalued level of the present cell accordingto multivalued levels of the preceding and ensuing cells.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationreproducing device reproducing a multivalued level from a reproductionsignal of a recording medium in which a mark representing information ofthe multivalued level is recorded on a cell, the device comprising, anA/D converting unit converting the reproduction signal into digitaldata, a digital-data retaining unit retaining the digital data, aprimary operation unit judging a multivalued level of the digital dataaccording to the reproduction signal deriving only from the mark of apresent cell, a judged-value retaining unit temporarily retaining thejudged multivalued level judged by the primary operation unit, anensuing cell level operation unit determining a multivalued level of anensuing cell ensuing the present cell prior to re-judging themultivalued level of the present cell, a reference judged valueselecting unit selecting either of the judged multivalued levels of apreceding cell preceding the present cell and the ensuing cell accordingto an amount of an inter-code interference from either of the precedingcell and the ensuing cell to the reproduction signal of the presentcell, and a re-judgment operation unit re-judging the multivalued levelof the present cell by referring to the judged multivalued levelselected by the reference judged value selecting unit.

According to the present invention, influences imposed by marks ofpreceding and ensuing cells on a multivalued-level judgment of a presentcell are determined from magnitudes of inter-code interferences so as toswitch judged multivalued levels to be used by the re-judgment operationunit in re-judging the multivalued level of the present cell. Therefore,even when a reproduction signal is subjected to the influences of themarks recorded on the preceding and ensuing cells, the multivalued levelof the present cell can be judged with less probability of erroneousjudgment.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention an informationrecording and reproducing device reproducing a multivalued level from areproduction signal of a writable recording medium in which a markrepresenting information of the multivalued level is recorded on a cell,the device comprising, an A/D converting unit converting thereproduction signal into digital data, a digital-data retaining unitretaining the digital data, a primary operation unit judging amultivalued level of the digital data according to the reproductionsignal deriving only from the mark of a present cell, a judged-valueretaining unit temporarily retaining the judged multivalued level judgedby the primary operation unit, an ensuing cell level operation unitdetermining a multivalued level of an ensuing cell ensuing the presentcell prior to re-judging the multivalued level of the present cell, areference judged value selecting unit selecting either of the judgedmultivalued levels of a preceding cell preceding the present cell andthe ensuing cell according to an amount of an inter-code interferencefrom either of the preceding cell and the ensuing cell to thereproduction signal of the present cell, a re-judgment-operation unitre-judging the multivalued level of the present cell by referring to thejudged multivalued level selected by the reference judged valueselecting unit, a learned-pattern recording unit recording allcombination patterns of a group of three marks as learned patterninformation of known multivalued levels in the recording medium, alearning unit reproducing the learned pattern information from therecording medium, and a criterion-table creating unit creating at leastone criterion table according to level-value information of thereproduction signal obtained from the learned pattern information by thelearning unit, the criterion table being used for judging themultivalued level of the present cell.

According to the present invention, a multivalued level of a presentcell is judged by using the criterion tables created according tolevel-value information of a reproduction signal obtained from thelearned pattern information; thereby, the above-described informationrecording and reproducing device according to the present invention canbe realized with ease. Additionally, the criterion tables are createdaccording to results of statistical processing applied to the learnedpattern information of known multivalued levels reproduced from therecording medium in which the learned pattern information is actuallyrecorded by the information recording and reproducing device beforehand.Thereby, disturbances, such as fluctuations in write/read optical powersand a distortion of a medium substrate, can be learned so as to createthe criterion tables enabling a correction of erroneous judgment due tothese disturbances.

Additionally, in the information recording and reproducing deviceaccording to the present invention, the learned-pattern recording unitmay record all the combination patterns outside a user data area in therecording medium.

According to the present invention, the learned pattern information ofknown multivalued levels can be recorded actually in the recordingmedium without affecting a user data area so that the learned patterninformation is used in creating the criterion tables.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention a recording mediumin which a mark representing information of a multivalued level isrecorded on a cell, wherein all combination patterns of a group of threemarks are recorded beforehand as learned pattern information of knownmultivalued levels so as to be used for creating at least one criteriontable used for judging the multivalued level.

According to the present invention, all combination patterns of a groupof three marks are recorded beforehand as learned pattern information ofknown multivalued levels in the so-called read-only recording medium. Byreproducing this learned pattern information from the recording medium,disturbances, such as fluctuations in write/read optical powers and adistortion of a medium substrate, can be learned so as to create thecriterion tables enabling a correction of erroneous judgment due tothese disturbances, as a result of which the criterion tables can beused appropriately in the multivalued-level judgment.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention a recording mediumin which a mark representing information of a multivalued level isrecorded on a cell, the recording medium comprising, a learned patterninformation area in which all combination patterns of a group of threemarks are recorded beforehand as learned pattern information of knownmultivalued levels so as to be used for creating at least one criteriontable used for judging the multivalued level, the learned patterninformation area being located outside a user data area.

According to the present invention, the so-called recordable recordingmedium includes a learned pattern information area in which allcombination patterns of a group of three marks are recorded beforehandas learned pattern information of known multivalued levels. By recordingthe learned pattern information in this learned pattern informationarea, and thereafter reproducing this learned pattern informationtherefrom, disturbances, such as fluctuations in write/read opticalpowers and a distortion of a medium substrate, can be learned so as tocreate the criterion tables enabling a correction of erroneous judgmentdue to these disturbances, as a result of which the criterion tables canbe used appropriately in the multivalued-level judgment.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1D are explanatory diagrams of an example of aninformation recording/reproducing method, including mark forms and areproduction signal, for the purpose of explaining principles ofembodiments according to the present invention;

FIG. 2 is a characteristic diagram representing a change of level of apresent cell caused by influences of preceding and ensuing cells;

FIG. 3 is a characteristic diagram representing a change of level of thepresent cell according as a level of a preceding cell;

FIG. 4 is a characteristic diagram representing a change of level of thepresent cell according as a level of an ensuing cell;

FIG. 5 is a characteristic diagram representing a change of level of thepresent cell according as levels of the preceding cell and the ensuingcell;

FIG. 6A is a characteristic diagram representing a change of level of acell having four even-number values;

FIG. 6B is a characteristic diagram representing a change of level of acell having four odd-number values;

FIG. 7 is a block diagram of an information recording/reproducing deviceaccording to a first embodiment of the present invention;

FIG. 8 is a block diagram of an example of a structure of amultivalued-level judging unit thereof;

FIG. 9 is an explanatory diagram illustrating an example of data in atable RAM shown in FIG. 8;

FIG. 10 is a block diagram of an information recording/reproducingdevice according to a second embodiment of the present invention;

FIG. 11 is a block diagram of an example of a structure of a digitalretaining unit thereof;

FIG. 12 is an explanatory diagram illustrating a present-cell judgmenttable and a creating method thereof;

FIG. 13A is an explanatory diagram illustrating a present-cell judgmenttable regarding a cell having four even-number values;

FIG. 13B is an explanatory diagram illustrating a present-cell judgmenttable regarding a cell having four odd-number values;

FIG. 14 is an explanatory diagram illustrating a preceding-cellreference table and a creating method thereof;

FIG. 15A is an explanatory diagram illustrating a preceding-cellreference table regarding a cell having four even-number values;

FIG. 15B is an explanatory diagram illustrating a preceding-cellreference table regarding a cell having four odd-number values;

FIG. 16 is an explanatory diagram illustrating an ensuing-cell referencetable and a creating method thereof;

FIG. 17A is an explanatory diagram illustrating an ensuing-cellreference table regarding a cell having four even-number values;

FIG. 17B is an explanatory diagram illustrating an ensuing-cellreference table regarding a cell having four odd-number values;

FIG. 18 is a flowchart outlining an example of a process of judging amultivalued level;

FIG. 19 is a flowchart of an example of a process of judging amultivalued level only based on a present cell;

FIG. 20 is a flowchart outlining an example of a process of judging amultivalued level according to a third embodiment of the presentinvention;

FIG. 21 is an explanatory diagram illustrating athree-successive-recording-mark learned table and a data extractingmethod thereof according to a fourth embodiment of the presentinvention;

FIG. 22 is a flowchart outlining an example of a process of judging amultivalued level;

FIG. 23 is an explanatory diagram symbolically illustrating a method forjudging a multivalued level according to a fifth embodiment of thepresent invention;

FIG. 24 is an explanatory diagram illustrating an error sum algorithmthereof;

FIG. 25 is an explanatory diagram symbolically illustrating a variationof the method for judging a multivalued level according to the fifthembodiment of the present invention;

FIG. 26 is an explanatory diagram illustrating an error sum algorithmthereof;

FIG. 27 is a flowchart outlining an example of a process of judging amultivalued level;

FIG. 28 is a block diagram of an information recording/reproducingdevice according to a sixth embodiment of the present invention;

FIG. 29 is a block diagram of an example of a structure of amultivalued-level judging unit thereof;

FIG. 30 is an explanatory diagram illustrating an example of data in atable RAM shown in FIG. 29;

FIG. 31 is a process transition diagram illustrating an example of aninformation reproducing process according to the sixth embodiment of thepresent invention;

FIG. 32 is a flowchart of the example of the information reproducingprocess according to the sixth embodiment of the present invention;

FIG. 33 is a block diagram of an example of a structure of amultivalued-level judging unit according to a seventh embodiment of thepresent invention;

FIG. 34A and FIG. 34B are explanatory diagrams illustrating an exampleof data in table RAMs shown in FIG. 33;

FIG. 35 is a process transition diagram illustrating an example of aninformation reproducing process according to the seventh embodiment ofthe present invention;

FIG. 36 is a flowchart of the example of the information reproducingprocess according to the seventh embodiment of the present invention;

FIG. 37 is a block diagram of an example of a structure of amultivalued-level judging unit according to an eighth embodiment of thepresent invention;

FIG. 38 is an explanatory diagram illustrating an example of data in atable RAM shown in FIG. 37;

FIG. 39 is a process transition diagram illustrating an example of aninformation reproducing process according to the eighth embodiment ofthe present invention;

FIG. 40 is a flowchart of the example of the information reproducingprocess according to the eighth embodiment of the present invention;

FIG. 41 is an explanatory diagram illustrating an example of data in atable RAM according to a ninth embodiment of the present invention;

FIG. 42 is a process transition diagram illustrating an example of aninformation reproducing process according to the ninth embodiment of thepresent invention;

FIG. 43 is a flowchart of the example of the information reproducingprocess according to the ninth embodiment of the present invention;

FIG. 44 is an explanatory diagram illustrating an example of data in atable RAM according to a tenth embodiment of the present invention;

FIG. 45 is a process transition diagram illustrating an example of aninformation reproducing process according to the tenth embodiment of thepresent invention; and

FIG. 46 is a flowchart of the example of the information reproducingprocess according to the tenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to the drawings, ofprinciples of embodiments according to the present invention.

FIG. 1A to FIG. 1D are explanatory diagrams of an example of aninformation recording/reproducing method according to the presentinvention. A tracking groove is formed on a surface of an informationrecording medium. A recording material allowing information recordedthereon to be erased is applied also on the information recordingmedium. Information is recorded as marks at predetermined time intervalson the recording medium. An area corresponding to each of thepredetermined time intervals is a unit of a multivalued informationrecording/reproduction referred to as an information cell (or simply, acell) 1. For example, when an information recording film composed ofphase change (PC) material is used as the recording-erasable recordingmaterial, a laser light is projected on this cell 1, and amounts andtimings of a recording light and an erasing light are adjusted so as tochange forms of the recording marks into recording marks at a pluralityof reproduction levels. FIG. 1A illustrates an example where the cells 1are recorded so as to have eight (=N) values at multivalued-levelsranging from level 0 with no recording mark to level 7 with a largestrecording mark. Each of the cells 1 includes 3-bit (=T-bit) information,because of (8=2³: N=2^(T), T=3). Reproducing the multivalued levels ofthe cells 1 as recorded results in a recording capacity three times aslarge as a normal optical disc on which 2-bit information is recorded.Besides, in order to increase the recording capacity, each of the cells1 needs to be made smaller. When each of the cells 1 is made smaller,marks of two to three cells 1 become encompassed within a diameter of areproducing beam, as shown in FIG. 1A.

Additionally, other than the phase change (PC) recording film, aninformation recording film composed of magneto-optical (MO) material canbe used as the above-mentioned recording-erasable recording material. Inthis case, an associated operation of a magnetic field applied from amagnetic head (not shown in the figure) with the above-mentioned laserlight changes the forms of the recording marks into the recording marksat a plurality of the reproduction levels. Further, a non-erasablerecording material allowing information to be only recorded andreproduced is also applicable. An organic dye or a metal film can beused as the non-erasable recording material. In this case, a laser lightis projected on the cell, and an amount and a timing of a recordinglight are adjusted so as to change the forms of the recording marks intothe recording marks at a plurality of the reproduction levels. Also, ina read-only recording medium used only for reproduction, recording markscan be formed on a substrate as uneven forms referred to as phase pits.In this case, a multivalued-level recording can be performed bymodulating an area or an optical depth of each of the phase pits.

Based on such multivalued-level recordings as described above, theprinciples of the embodiments according to the present invention will bedescribed hereinbelow by taking the case using the phase changerecording film, as an example.

Here, an actual example of multi-value recording/reproduction will bedescribed. In this example, the multi-value recording/reproduction isrealized by a rewritable-DVD recording device used in general. Arecording/reproducing wavelength λ is 650 nm; a numerical aperture (NA)of an objective lens is 0.65. A diameter of a light converged on anoptical information recording medium (a recording medium) isapproximately 0.8 μm. A rewritable type of a phase change materialAgInSbTe is used as the optical information recording medium. Recordingmarks are formed on a groove. An interval (a track pitch) betweenadjacent grooves is 0.74 μm. A width of the groove is approximately 0.4μm. A linear velocity of recording/reproducing is approximately 3.5 m/s.A length of the cell 1 in a circumferential direction of the disc isapproximately 0.6 Wm. An erase power is set 0.5 to 0.6 times as much asa record (write) power. The number (N) of levels of multivaluedinformation is set at 8.

First, FIG. 2 shows a result of recording and reproducing randominformation. In FIG. 2, the axis of ordinates represents a normalizedmultivalued signal which is obtained by normalizing a reproduction levelat the center of each cell 1 by a difference between a level (max) of ahighest reflectance with no recording mark and a level (min) at which amark is so recorded that a catoptric amount becomes lowest. Assumingthat RF represents a reproduction signal, the normalized multivaluedsignal can be expressed as follows.(Normalized multivalued signal)=(RF−min)/(max−min)  (1)

According to the result shown in FIG. 2, the reproduction (reproduced)signal does not perfectly represent one of the eight values. Therefore,upon judging a level of the reproduction signal from level 0 to level 7,there may occur an instance where the reproduction signal is reproducedat level 2, despite having been recorded at level 1, for example. Thislevel-judgment error is originated from an inter-code interferencephenomenon caused by recording marks of the preceding and ensuing cells1 being encompassed within the reproducing beam, resulting in thereproduction level of the present cell 1 being varied according as sizesof the recording marks of the preceding and ensuing cells 1.

By contrast, in FIG. 3, the data shown in FIG. 2 is divided according toknown multivalued levels of the preceding cell (represented by the axisof abscissas in FIG. 3: preceding levels). FIG. 3 illustrates how thereproduction level of the present cell is varied according as thepreceding levels. According to the result shown in FIG. 2, a multivaluedlevel cannot be determined uniquely from the reproduction signal.However, by learning relationships between multivalued levels of thepreceding cell and multivalued levels of the present cell beforehand,storing the relationships as criteria for judging multivalued levels,and dividing the relationships according to the preceding levels of thepreceding cell, a multivalued level of the present cell can bedetermined uniquely. A “first principle” of the present invention usesthis principle: by “preparing criteria for judging multivalued levels ofa present cell according to multivalued-level data of a preceding cell,and switching the criteria for judging the present cell after judging amultivalued level of the preceding cell so as to judge a multivaluedlevel of the present cell,” the level-judgment error originated from theinter-code interference phenomenon occurring in the state as shown inFIG. 2 can be prevented.

Similarly, in FIG. 4, the data shown in FIG. 2 is divided according tomultivalued levels of the ensuing cell (represented by the axis ofabscissas in FIG. 4: ensuing levels). FIG. 4 illustrates how thereproduction level of the present cell is varied according as theensuing levels. By learning relationships between multivalued levels ofthe ensuing cell and multivalued levels of the present cell beforehand,storing the relationships as criteria for judging multivalued levels,and dividing the relationships according to the ensuing levels of theensuing cell, a multivalued level of the present cell can be determineduniquely. A “second principle” of the present invention uses thisprinciple: by “preparing criteria for judging multivalued levels of apresent cell according to multivalued-level data of an ensuing cell, andswitching the criteria for judging the present cell after judging amultivalued level of the ensuing cell so as to judge a multivalued levelof the present cell,” the level-judgment error originated from theinter-code interference phenomenon occurring in the state as shown inFIG. 2 can be prevented.

Further, when multivalued levels of the preceding and ensuing cellspreceding and ensuing the present cell are learned respectively, levelsof the multivalued reproduction signal are not spread, as shown in FIG.5; thus, a multivalued level can be determined uniquely from thereproduction signal. It is noted that FIG. 5 shows multivalued levels ofthe present cell when the ensuing level is zero, and the precedinglevels range from 0 to 7. A “third principle” of the present inventionuses this principle: by “preparing criteria for judging multivaluedlevels of a present cell according to multivalued-level data ofpreceding and ensuing cells, and switching the criteria for judging thepresent cell after judging a cell level of the preceding cell and a celllevel of the ensuing cell so as to judge a multivalued level of thepresent cell,” the level-judgment error originated from the inter-codeinterference phenomenon occurring in the state as shown in FIG. 2 can beprevented. In other words, the third principle of the present inventionis a combination of the first principle and the second principle of thepresent invention.

Table 1 below shows results of level judgments actually performed basedon the reviews of the criteria for judging multivalued levels accordingto the first to third principles of the present invention. In No. 2 andNo. 8, levels of the present cell are judged to be “0” according toreproduction signal values of the present cell, which are erroneousjudgments in light of correct levels “1”. However, by referring tovalues in a preceding-level table including criteria for judgingmultivalued levels according to levels of the preceding cell, or byreferring to values in an ensuing-level table including criteria forjudging multivalued levels according to levels of the ensuing cell, thelevels of the present cell are judged to be “1” in No. 2 and No. 8,which are correct judgments. TABLE 1 Normalized Present Preceding-Ensuing- Error Correct reproduction cell level table level tablejudgment No. level signal Value Judgment Value Judgment Value JudgmentValue Judgment 1 4 0.37545 4 4 4 4 2 1 0.84738 0 err 1 1 1 3 2 0.61683 22 2 2 4 4 0.33477 4 4 4 4 5 7 0.05081 7 7 7 7 6 0 0.88015 0 0 0 0 7 50.24922 5 5 5 5 8 1 0.84841 0 err 1 1 1 9 2 0.67702 2 2 2 2 10 0 0.953840 0 0 0 11 0 0.95784 0 0 0 0 12 2 0.65826 2 2 2 2 13 2 0.68140 2 2 2 214 2 0.61079 2 2 2 2 15 6 0.14009 6 6 6 6 16 4 0.36896 4 4 4 4 23 50.25405 5 5 5 5 24 2 0.66783 2 2 2 2 25 2 0.58196 3 err 3 err 2 2 26 70.06542 7 7 7 7 27 4 0.39899 4 4 4 4 227 7 0.04583 7 7 7 7 228 6 0.107226 6 6 6 229 0 0.84590 1 err 1 err 0 0 230 6 0.17278 6 6 6 6 231 60.17744 6 6 6 6

However, further according to the judgment results shown in Table 1,there are cases in which a level judged by referring to thepreceding-level table and a level judged by referring to theensuing-level table do not coincide. This phenomenon can be observed inNo. 25 in Table 1 above, in which the level judged by referring to thepreceding-level table is “3” which is incorrect, and the level judged byreferring to the ensuing-level table is “2” which is correct. Examiningmany similar phenomena as the above-mentioned phenomenon revealstendencies as follows.

Assuming that a combination of the three successive cells 1 isrepresented by (X, Y, Z) with Y being multivalued-level data of thepresent cell, the following cases {circle around (1)} and {circle around(2)} apply.

{circle around (1)} It is under a relationship of (X>Z) that a level ofY is judged correctly at a high probability by referring to thepreceding-level table.

{circle around (2)} It is under a relationship of (X<Z) that a level ofY is judged correctly at a high probability by referring to theensuing-level table.

It is noted that each of multivalued levels represented by X, Y and Zbecomes larger as an area of a mark recorded on the cell 1 becomeslarger. In No. 25 in Table 1, (X, Y, Z) is (2, 2, 7), which satisfiesthe relationship of (X<Z), corresponding to the case {circle around(2)}. In this case, the level judged by referring to the ensuing-leveltable is “2” which is correct; thus, a multivalued-level judgmentcorrectly judging the level of the present cell can be selected. Thisconstitutes a “fourth principle” of the present invention. Thisphenomenon is governed by the principle that “one of a preceding celland an ensuing cell that includes a recording mark having a larger areaposes a larger amount of inter-code interference manifested as anoptical influence on a present cell.”

Next, a description will be given of a principle of a level judgmentunder a relationship other than the relationships set forth in theabove-mentioned cases {circle around (1)} and {circle around (2)}, undera relationship of (X=Z). In No. 229 in Table 1 above, (X, Y, Z) is (6,1, 6), which corresponds to the case of (X=Z). In this case, a leveljudged by referring to the preceding-level table is “1” which isincorrect, and a level judged by referring to the ensuing-level table is“0” which is correct.

In the above-mentioned relationships shown in FIG. 3 and FIG. 4, adistribution of combinations of a preceding level being “0” and a levelof the present cell (named center level in the figures) being “0”, forexample, has a fluctuation band due to an influence of a recording markof the ensuing cell. An average (a normalized reproduction signal value)of these distributed combinations of (X=0, Y=0, Z=any value) is treatedas one of learned results (the preceding-level table) learned in caseswhere judged values of recording marks of the ensuing cell are unknown,according to a statistical work ignoring the judged values of therecording marks of the ensuing cell.

A specific expression is expressed as follows:LR(Xi,Yj)=[Total sum of normalized reproduction signal values ofcombinations (Xi,Yj)]/[Number of combinations (Xi,Yj)]

In this expression, Xi and Yj represent levels in a range thatmultivalued-level signals can assume; in the eight-value recording, therange is expressed as (0≦Xi, Yj≦7).

Similarly, as to the ensuing-level table, a specific expression isexpressed as follows:LR(Yi,Zj)=[Total sum of normalized reproduction signal values ofcombinations (Yi,Zj)]/[Number of combinations (Yi,Zj)]

It is preferred that these learned results are obtained beforehand byreproducing an area in which all of known combination patterns of thethree successive cells 1 are recorded, and performing the statisticalprocessing.

These learned results obtained beforehand, i.e., learned results forpreceding-level table: LR (Xi, Yj); and

learned results for ensuing-level table: LR (Yi, Zj),

are hereinafter expressed as “ideal values”. In the case of (X=Z),assuming that an actually measured reproduction signal value is y, thatan ideal value calculated from the learned results for thepreceding-level table is y1, and that an ideal value calculated from thelearned results for the ensuing-level table is y2, selecting a judgmentresult involving a smaller error with respect to the ideal value enablesa correct level judgment at a high probability, even in the case of(X=Z). This additional principle is referred to as a “fifth principle”of the present invention.

Specifically, in No. 229 in Table 1 created from actually measured data,y is 0.84590, y1 is 0.900420, and y2 is 0.894110; thus, respectiveerrors satisfy the following magnitude relation.|y−y1|=0.054521 (absolute value as to the preceding-level tableresult)>|y−y2|=0.048209 (absolute value as to the ensuing-level tableresult)

Accordingly, a judgment result of the ensuing-level table involving thesmaller error with respect to the ideal value can be selected. Asdescribed above, judging a multivalued level of the present cell byusing the fourth principle and the fifth principle of the presentinvention can further enhance a probability of correctly judging themultivalued level, compared with the level judgment by referring only tothe preceding-level table or the ensuing-level table.

Besides, when a reproduction signal cannot be judged uniquely to be oneof the eight-value levels as shown in FIG. 2, reducing the number ofmultivalues of recording marks enables a unique judgment, as shown inFIG. 6A and FIG. 6B. FIG. 6A shows an example where a lowest-order bitamong the three (=T) bits is fixed at 0 so as to reduce the eight (=N)values down to four (=M=2^(T−1)) values. FIG. 6B shows an example wherea lowest-order bit among the three (=T) bits is fixed at 1 so as toreduce the eight (=N) values down to four (=M=2^(T−1)) values. That is,instead of a uniform recording with N-valued marks, FIG. 6A and FIG. 6Aindicate recording methods in each of which an M-valued mark is recordedon one cell in every predetermined number (=three) of cells so as tointervene between the N-valued marks. A “sixth principle” of the presentinvention uses this principle.

According to the above-mentioned first principle, in the course ofrepeatedly reproducing each present cell based on information of apreceding cell, erroneously reading the preceding cell due to a defectand so forth passes the error on to a following cell, possibly leadingto successive erroneous reading of following cells. Thereupon, as shownin FIG. 1C, an M-valued mark with a reduced number of multivalued levelsis recorded on one cell in every predetermined number (=n) of cells suchthat the cell with the reduced number of the multivalued levels isreproduced independently, and each of the other cells (the cells withN-valued marks) is reproduced based on level information of precedingand ensuing cells; thereby, successive erroneous reading of followingcells can be prevented. In an example shown in FIG. 1C and FIG. 1D, datais recorded as a combination of an eight-valued mark, an eight-valuedmark and a four-valued mark, and is reproduced as the combination of theeight-valued mark, the eight-valued mark and the four-valued mark. (Inreality, either of marks “000”, “010”, “100” and “110” is recorded on afour-valued cell, and is reproduced with the lowest-order bit “0” beingomitted, as shown in FIG. 1D. Accordingly, successive errors can beprevented.

Thus preventing successive errors of judgments, and further increasing arecording density with the length of the cell in the circumferentialdirection shortened to approximately 0.45 μm, starts to yield resultscontradicting the fourth principle and the fifth principle of thepresent invention. A cause thereof is a sampling timing error uponsubjecting a multivalued-level signal of each of the cells 1 to an A/Dconversion. Due to the sampling error, a sampling cannot be performed atthe center of the cell 1 such that a balance of the inter-codeinterference becomes deviated from an ideal state. Accordingly, errorsbecome likely to occur in level judgment results of a cell judged onlyby the present cell. Under these conditions, for the purpose ofincreasing a probability of correct judgment, the fourth principle isimproved as follows.

The following results are obtained from learning of the preceding-leveltable and the ensuing-level table:

learned results for preceding-level table: LR (Xi, Yj); and

learned results for ensuing-level table: LR (Yi, Zj).

Assuming that an actually measured reproduction signal value is y, thatan ideal value calculated from the learned results for thepreceding-level table is y1, and that an ideal value calculated from thelearned results for the ensuing-level table is y2, selecting a judgmentresult involving a smaller error with respect to the ideal value enablesa correct level judgment at a high probability. This improved fourthprinciple is referred to as a “seventh principle” of the presentinvention. TABLE 2 Normalized Present Preceding- Ensuing- Error Correctreproduction cell level table level table judgment No. level signalValue Judgment Value Judgment Value Judgment Value Judgment 1 4 0.380994 4 4 4 2 1 0.84247 1 1 1 1 3 2 0.71666 2 2 2 2 103 1 0.77924 1 1 1 1104 6 0.18137 6 6 6 6 105 6 0.16647 6 6 6 6 106 1 0.82589 1 0 err 1 1107 1 0.78905 1 1 1 1 108 2 0.63709 2 2 2 2 109 6 0.18721 6 6 6 6 200 00.90720 0 0 0 0 201 6 0.13970 6 6 6 6 202 1 0.84643 0 err 0 err 1 1 2033 0.53928 3 3 3 3 204 2 0.69804 2 2 2 2 205 6 0.15893 6 6 6 6

Specifically, in No. 106 in Table 2 created from actually measured data,y is 0.82589, y1 is 0.878425, and y2 is 0.798644; thus, respectiveerrors satisfy the following magnitude relation.|y−y1|=0.052538 (absolute value as to the preceding-level tableresult)>|y−y2|=0.027242 (absolute value as to the ensuing-level tableresult)

Accordingly, a judgment result of the ensuing-level table involving thesmaller error with respect to the ideal value can be selected, and thejudgment result is correct. Additionally, in No. 202 in Table 2, y is0.84643, y1 is 0.878425, and y2 is 0.821804; thus, respective errorssatisfy the following magnitude relation.|y−y1|=0.031990 (absolute value as to the preceding-level tableresult)>|y−y2|=0.024631 (absolute value as to the ensuing-level tableresult)

Accordingly, a judgment result of the ensuing-level table involving thesmaller error with respect to the ideal value can be selected, and thejudgment result is correct.

As in these two examples, judging a multivalued level of the presentcell by using the seventh principle of the present invention can furtherenhance a probability of correctly judging the multivalued level,compared with the combination of the fourth principle and the fifthprinciple. However, the seventh principle always necessitates an errorjudgment, which increases a calculation amount, in contrast to thefourth principle and the fifth principle; thus, the seventh principlerequires a high calculation speed. Besides, using a result re-judged andfed back according to the principles of the present invention further inre-judgment can reduce a probability of erroneous judgment.

Hereinbelow, descriptions will be given of the embodiments based on theabove-described principles according to the present invention.

First, a description will be given, with reference to FIG. 7 to FIG. 9,of a first embodiment according to the present invention. The presentfirst embodiment adopts the first principle of the present invention.

FIG. 7 is a block diagram used for explaining a structure and anoperation of an information recording/reproducing device according tothe present first embodiment. While an information recording medium 3 isbeing revolved by a spindle motor 2, a laser beam emitted from a LD(laser diode) 4 is projected along a track on the information recordingmedium 3 by an optical head 5. A reflected light from the informationrecording medium 3 is detected by a PD (photodetector) 6, and issubjected to a focus/tracking control by an OP amplifier 7 and a servocircuit 8 so as to stably project the laser beam on the informationtrack. Additionally, a reproduction signal “a” detected by, the PD 6 isamplified by an RF amplifier 9, and thereafter, is converted intodigital data c by a digital data converting unit 12 consisting of asector synchronization detecting unit 10 and an A/D converting unit 11.

Besides, although not shown in FIG. 7, the digital data c is subjectedto a normalization process as described above so that a value ofreproduced digital data does not fluctuate. In FIG. 2, the normalizationprocess is conducted such that a maximum level becomes “1”, for the sakeof easy comprehension. In FIG. 7, the digital data is normalized tobecome an integral value so that the data can be easily processedthenceforth. When the digital data is processed as 10-bit digital data,the digital data is normalized as follows.(Normalized digital data)=[(RF−min)/(max−min)]×1024  (2)

This digital data c is detected and converted by a multivalued-leveljudging unit 13 into cell level data e corresponding to a multivaluedlevel of each of the cells 1. The cell level data e is converted intoreproduction information g by a cell-data converting unit 14. Thus,information is reproduced from the information recording medium 3 onwhich multivalued information is recorded.

On the other hand, upon recording, input information h is converted by amultivalued-level converting unit 15 into the cell level data e, andsignals representing light intensities and timings of recording anderasing pulses are generated by a recording pulse generating unit 16,and are supplied to an LD drive circuit 17. Thereby, a recording mark isrecorded on the information recording medium 3 by the LD 4. The LD 4,the LD drive circuit 17, the recording pulse generating unit 16, andother components together form a recording unit.

With the above-described structure, the present first embodiment, usingthe first principle, changes criteria for judging a present cell by ajudging-criteria changing unit according to a preceding cell level so asto prevent a level-judgment error. Therefor, the multivalued-leveljudging unit 13 comprises an operation unit 18 judging a cell level, anda cell level retaining unit (a multivalued level data retaining unit) 19retaining the cell level data of a preceding cell, as shown in FIG. 8.The operation unit 18 comprises a table RAM 20 storing level datacorresponding to each input digital data (each reproduction level), andan address generating unit 21 reading the cell level data e from thetable RAM 20, according to a preceding cell level f and a value of thedigital data c.

The table RAM 20 functioning as the judging-criteria changing unitstores cell level data at addresses corresponding to values of thedigital data c, the cell level data being divided according to celllevel data of a preceding cell, as shown in FIG. 9. Thus, for example,when the cell level data of the preceding cell is “2”, and the digitaldata is “131”, cell level data “1” is read from an address of“2*1024+131”. That is, by adding an offset generated from the cell leveldata of the preceding cell to the address of the digital data andreading from the address, criteria for judging the cell level can bechanged according to the preceding cell so as to generate the cell levelthereby. This 3-bit cell level data row reproduced from each cell iscollected by the cell-data converting unit 14 so as to form thereproduction information g which is an 8-bit data row. Accordingly,whereas a micro cell, three of which become encompassed within areproducing beam, conventionally causes a reproduction error due to aninfluence of the inter-code interference when reproduced cell by cell,such a micro cell can be reproduced without an error according to thepresent embodiment.

Besides, the table RAM 20 initially stores the cell level data asfollows: cell level data of all combinations of three cells (8*8*8=512combinations) are recorded beforehand on an area other than a user dataarea, such as a lead-in area, on the recording medium 3; the cell leveldata is reproduced so as to obtain a cell level of each combination ofthe three cells; and the cell levels are recorded on the table RAM 20before reproducing the user data. Alternatively, a table containing thecell level data may be prepared beforehand; in this case, offset valuesare adjusted, for example, at level 0 to cancel such factors as areflectance alteration.

Next, a description will be given, with reference to FIG. 10 to FIG. 19,of a second embodiment according to the present invention. The presentsecond embodiment is an example of applying the present invention to amulti-value (eight-value) recording in which user data is recorded as acombination of an eight-valued mark, an eight-valued mark and afour-valued mark, as in the example shown in FIG. 1C and FIG. 1D. Thepresent second embodiment uses the fourth and fifth principles injudging a multivalued level, which switches criteria for judging a celllevel of a present cell by referring to a cell level of a preceding celland a cell level of an ensuing cell so as to prevent a level-judgmenterror.

FIG. 10 is a block diagram used for explaining a structure of aninformation recording/reproducing device according to the present secondembodiment. The structure of the information recording/reproducingdevice shown in FIG. 10 is basically the same as the structure of theinformation recording/reproducing device shown in FIG. 7 except thefollowing points. The reproduction signal “a” detected by the PD 6 isamplified by the RF amplifier 9, and the inter-code interference issuppressed by a waveform equalization circuit (not shown in the figure).Thereafter, the reproduction signal “a” is converted into digital data cby a digitizing unit 24 consisting of a sampling-synchronizationdetecting unit 22 and an A/D converting unit 23. In the presentembodiment, though not shown in FIG. 10, the digital data c is subjectedto a normalization process as described above so that a value ofreproduced digital data does not fluctuate. In the present embodiment,the digital data is normalized also by the above-described expression(2).

This digital data c is temporarily stored in a digital retaining unit (adigital-data retaining unit) 25 so that signal data e of groups ofsampled cells can be selectively read on an individual cell basis by aCPU 26.

At this point, for the purpose of reproducing multivalued data, threecriterion tables (a present-cell judgment table 29, a preceding-cellreference table 33, an ensuing-cell reference table 35) used for judgingmultivalued levels are created. In the eight-value recording,combinations of three successive cells total (8³=512). Thereupon, allcombination patterns of a group of three marks (cells) are recorded aslearned pattern information of known multivalued levels by alearned-pattern recording unit (not shown in the figure) on an innermostarea of the recording medium 3 on which user data is not recorded.Thereafter, the learned pattern information is reproduced by a learningunit (not shown in the figure), and the digital data c sampled at acentral cell of the three successive cells is temporarily stored in thedigital retaining unit 25. The data is stored in a temporary storage RAM27 provided in the digital retaining unit 25 show in FIG. 11 in anarrangement shown in FIG. 12. The data can be selectively read bydesignating an address of the data in the temporary storage RAM 27 by anaddress generating unit 28.

First, based on the information stored in the temporary storage RAM 27,the present-cell judgment table 29 ignoring (preceding) levels of apreceding cell and (ensuing) levels of an ensuing cell is created. Forexample, regarding the cell level of the present cell being “0”, thereare 64 combinations (8 values for the preceding level times 8 values forthe ensuing level). A criterion signal y0 used in judging each level iscalculated as an average of these 64 combinations. Also, regarding thecell level of the present cell being “1” to “7”, the criterion signal y0is calculated similarly so as to create the present-cell judgment table29 as shown in FIG. 12. In the structure shown in FIG. 10, the learnedpatterns (the 512 combinations) stored in the temporary storage RAM 27are read in succession, and are subjected to the above-describedcalculation by the CPU 26, results of which are recorded on a RAM 30.This process is performed by the CPU 26 as a function of acriterion-table creating unit.

Besides, present-cell judgment tables 32 a and 32 b regarding afour-value cell can be created similarly. The present-cell judgmenttable 32 a shown in FIG. 13A corresponds to the example shown in FIG. 6Awhere each of the four values is an even number. The present-celljudgment table 32 b shown in FIG. 13B corresponds to the example shownin FIG. 6B where each of the four values is an odd number.

Next, a description will be given of a method for creating thepreceding-cell reference table 33. The signal data e of sampled cellsobtained from recordings of all combinations of three successive cellsis selectively read, as in creating the present-cell judgment table 29.The preceding-cell reference table 33 ignoring levels of an ensuing cellis created as follows.

FIG. 14 is a diagram used for explaining the method for creating thepreceding-cell reference table 33. For example, regarding combinationswhen the cell level of the preceding cell being “0” and the cell levelof the present cell being “0”, eight items of data circled by ◯ amongthe data temporarily stored in the temporary storage RAM 27 in the samearrangement as shown in FIG. 12 are subjected to an average process soas to calculate a criterion signal y1 used in judging the cell level. Asa result of this, the preceding-cell reference table 33 containing 64combinations ignoring levels of an ensuing cell can be created. Also,regarding the cell level of the present cell being “1” to “7”, thecriterion signal y1 is calculated similarly so as to create the table asshown in FIG. 14. In the structure shown in FIG. 10, the learnedpatterns (the 512 combinations) stored in the temporary storage RAM 27are read in succession, and are subjected to the above-describedcalculation by the CPU 26, results of which are recorded on the RAM 30.This process is performed by the CPU 26 as a function of thecriterion-table creating unit.

Besides, preceding-cell reference tables 34 a and 34 b regarding afour-value cell can be created similarly. The preceding-cell referencetable 34 a shown in FIG. 15A corresponds to the example shown in FIG. 6Awhere each of the four values is an even number. The preceding-cellreference table 34 b shown in FIG. 15B corresponds to the example shownin FIG. 6B where each of the four values is an odd number.

Further, a description will be given of a method for creating theensuing-cell reference table 35. The signal data e of sampled cellsobtained from recordings of all combinations of three successive cellsis selectively read, as in creating the present-cell judgment table 29.The ensuing-cell reference table 35 ignoring levels of a preceding cellis created as follows.

FIG. 16 is a diagram used for explaining the method for creating theensuing-cell reference table 35. For example, regarding combinationswhen the cell level of the ensuing cell being “0” and the cell level ofthe present cell being “0”, eight items of data circled by ◯ among thedata temporarily stored in the temporary storage RAM 27 in the samearrangement as shown in FIG. 12 are subjected to an average process soas to calculate a criterion signal y2 used in judging the cell level. Asa result of this, the ensuing-cell reference table 35 containing 64combinations ignoring levels of a preceding cell can be created. Also,regarding the cell level of the present cell being “1” to “7”, thecriterion signal y2 is calculated similarly so as to create the table asshown in FIG. 16. In the structure shown in FIG. 10, the learnedpatterns (the 512 combinations) stored in the temporary storage RAM 27are read in succession, and are subjected to the above-describedcalculation by the CPU 26, results of which are recorded on the RAM 30.This process is performed by the CPU 26 as a function of thecriterion-table creating unit.

Besides, ensuing-cell reference tables 36 a and 36 b regarding afour-value cell can be created similarly. The ensuing-cell referencetable 36 a shown in FIG. 17A corresponds to the example shown in FIG. 6Awhere each of the four values is an even number. The ensuing-cellreference table 36 b shown in FIG. 17B corresponds to the example shownin FIG. 6B where each of the four values is an odd number.

A description will be given of a method for judging a multivalued levelby using the combination of the fourth principle and the fifthprinciple, which refers to the RAM 30 on which the learned results (thepresent-cell judgment table 29, the preceding-cell reference table 33,the ensuing-cell reference table 35) obtained as above are: recorded.FIG. 18 is a flowchart outlining an example of a process of judging amultivalued level performed by the CPU 26 according to the combinationof the fourth principle and the fifth principle.

A data row of the cell 1 is digitized on an individual cell basis, andis temporarily stored in the temporary storage RAM 27, as a digitizedsignal value y. Here, reading of digital data SLn−1 of a preceding cellCn−1 preceding a present cell Cn (step S1), judging of a cell levelCLn−1 thereof (step S2), reading of digital data SLn of the present cellCn (step S3), judging of a cell level CLn thereof (step S4), reading ofdigital data SLn+1 of an ensuing cell Cn+1 ensuing the present cell Cn(step S5), judging of a cell level CLn+1 thereof (step S6), areperformed successively. In the step S4, the cell level CLn closest tothe value y is determined in the present-cell judgment table 29; thisprocess in the step S4 is performed as a function of a primary operationunit. Additionally, the process in the step S6 is performed as afunction of an ensuing cell-level operation unit. Then, the cell leveldata CLn and the signal value y are written to a RAM 31, which functionsas a judged-value retaining unit, by specifying addresses such that arelation therebetween is known.

Subsequently, three consecutive items of the cell level information(CLn−1, CLn, CLn+1) and the digitized signal value y of the present cellCn are read from the RAM 31, and magnitudes of the cell levels CLn−1 andCLn+1 are compared according to the fourth principle and the fifthprinciple step S7) so as to perform a re-judgment process regarding thepresent cell Cn.

At this point, as a result of the comparison, when CLn−1>CLn+1, apresent-cell level value having the value y1 closest to the digital dataSLn is determined as a judged level value DL of the present cell Cn byreferring to the preceding-cell reference table 33 (step S8). Otherwise,as a result of the above-mentioned comparison, when CLn−1<CLn+1, apresent-cell level value having the value y2 closest to the digital dataSLn is determined as the judged level value DL of the present cell Cn byreferring to the ensuing-cell reference table 35 (step S9).

On the other hand, as a result of the above-mentioned comparison, whenCLn−1=CLn+1, a present-cell level value having the value y1 closest tothe digital data SLn is provisionally determined as a judged level valueDL1 of the present cell Cn by referring to the preceding-cell referencetable 33, and a present-cell level value having the value y2 closest tothe digital data SLn is provisionally determined as a judged level valueDL2 of the present cell Cn by referring to the ensuing-cell referencetable 35 (step S10). Then, magnitudes of these judged level values DL1and DL2 are compared. When DL1=DL2, either of DL1 and DL2 is arbitrarilyselected as the judged level value DL of the present cell Cn (step S11)so as to settle the cell level CLn of the present cell Cn at DL, andrewrite the settled DL to the RAM 31 (step S12).

Otherwise, when DL1≠DL2, according to a magnitude relation between|y−y1| and |y−y2|, when |y−y1|<|y−y2|, DL1 is selected as the judgedlevel value DL of the present cell Cn; when |y−y1|>|y−y2|, DL2 isselected as the judged level value DL of the present cell Cn (step S13);thus, the cell level CLn of the present cell Cn is settled at DL, andthe settled DL is rewritten to the RAM 31 (step S12) Processes of thesesteps S7 to S13 are performed as functions of a reference judged valueselecting unit and a re-judgment operation unit.

Besides, as shown in FIG. 19, regarding a cell of a four-valued level, acell level of the present cell is judged only from the present cell perse, as follows: digital data SLn of the present cell Cn is read (stepS21), and a cell level value having the value y0 closest to the value yis determined as a judged value DLn by referring to the present-celljudgment table 32 a or 32 b (step S22).

Successively, judging multivalued levels of the following cells by usingthe multivalued data rewritten as above can further decrease aprobability of erroneous judgment.

Besides, readings and writings from/to the RAMs 27, 30 and 31 and otheroperational processes are timed in synchronization with a samplingtiming by the sampling-synchronization detecting unit 22 shown in FIG.10.

Next, a description will be given, with reference to FIG. 20, of a thirdembodiment according to the present invention. The present thirdembodiment is an example of applying the present invention to amulti-value (eight-value) recording in which user data is recorded as acombination of an eight-valued mark, an eight-valued mark and afour-valued mark, as in the example shown in FIG. 1C and FIG. 1D. Thepresent third embodiment uses the seventh principle in judging amultivalued level so as to prevent a level-judgment error. Additionally,the present third embodiment uses the information recording/reproducingdevice shown in FIG. 10, and also creates the three criterion tables(the present-cell judgment table 29, the preceding-cell reference table33, the ensuing-cell reference table 35) used for performing amultivalued-level judgment, as does the foregoing second embodiment.

A description will be given, with reference to a flowchart shown in FIG.20, of a method for judging a multivalued level according to the seventhprinciple by referring to the RAM 30 on which the learned results (thepresent-cell judgment table 29, the preceding-cell reference table 33,the ensuing-cell reference table 35) are recorded. Processes in steps S1to S6 shown in FIG. 20 are performed in the same manner as in the stepsS1 to S6 shown in FIG. 18.

After the step S6, a provisional judgment process is performed in whicha present-cell level value having the value y1 closest to the digitaldata SLn is provisionally determined as a judged level value DL1 of thepresent cell Cn by referring to the preceding-cell reference table 33,and a present-cell level value having the value y2 closest to thedigital data SLn is provisionally determined as a judged level value DL2of the present cell Cn by referring to the ensuing-cell reference table35 (step 531). Thereafter, magnitudes of the cell levels CLn−1 and CLn+1are compared (step S32) so as to perform a re-judgment process regardingthe present cell Cn.

As a result of the comparison, when |y−y1|=|y−y2|, the judged levelvalue is kept to be the original cell level CLn (step S33). When|y−y1|<|y−y2|, DL1 is selected as the judged-level value DL of thepresent cell Cn (step S34) so as to settle the cell level CLn of thepresent cell Cn at DL, and rewrite the settled DL to the RAM 31 (stepS35). When |y−y1|>|y−y2|, DL2 is selected as the judged level value DLof the present cell Cn (step S36) so as to settle the cell level CLn ofthe present cell Cn at DL, and rewrite the settled DL to the RAM 31(step S35).

Successively, judging multivalued levels of the following cells by usingthe multivalued data rewritten as above can further decrease aprobability of erroneous judgment.

Besides, readings and writings from/to the RAMs 27, 30 and 31 and otheroperational processes are timed in synchronization with the samplingtiming by the sampling-synchronization detecting unit 22 shown in FIG.10.

Table 3 shows results of comparing degrees of effects of the second andthird embodiments with that of a level judgment based only on a presentcell. Error rates shown in Table 3 are on an individual cell basis.Besides, a recording density depends on a cell length such that theshorter the cell length is, the higher the recording density is. TABLE 3Cell Present cell 4^(th) + 5^(th) principle 7^(th) principle lengthjudgment judgment judgment 0.56 2.25 0.42 0.17 0.45 5.68 2.76 1.42 0.4010.90 6.85 4.67 μm %

According to the results shown in Table 3, although reduction effects oferror rates vary depending on the recording densities, it is understoodthat the error judgment rate on an individual cell basis is reduced byapproximately 0.2-0.6 times according to the combination of the fourthprinciple and the fifth principle, and that the error judgment rate isreduced by approximately 0.1-0.4 times according to the seventhprinciple.

As described above, upon judging a level of a present cell byassociating the level with cell information of a preceding cell and anensuing cell preceding and ensuing the present cell, it has beenconfirmed that an erroneous judgment can be largely improved accordingto the “combination of the fourth principle and the fifth principle” andthe “seventh principle”.

Next, a description will be given, with reference to FIG. 21 and FIG.22, of a fourth embodiment according to the present invention. Thepresent fourth embodiment is an example of applying the presentinvention to a multi-value (eight-value) recording in which user data isrecorded as a combination of an eight-valued mark, an eight-valued markand a four-valued mark, as in the example shown in FIG. 1C and FIG. 1D.However, in the present fourth embodiment, a method for judging amultivalued level is not a method of switching the reference tables asdescribed above, but is a method of judging according to a resultlearned from all patterns of combinations of three successive recordingmarks. FIG. 21 shows an example of a learned table 37 according to thepresent fourth embodiment. This learned table 37 is in a state prior tocalculating the above-described three tables (the present-cell judgmenttable 29, the preceding-cell reference table 33, theensuing-cell-reference table 35). Hereinbelow, this learned table 37 isalso referred to as a three-successive-recording-mark learned table.

A description will be given, with reference to a flowchart shown in FIG.22, of a method for judging a multivalued level by referring to the RAM30 on which the learned result (the three-successive-recording-marklearned table 37) is recorded. Processes in steps S1 to S6 shown in FIG.22 are performed in the same manner as in the steps S4 to S6 shown inFIG. 18 and FIG. 20.

After the step S6, upon performing a re-judgment of a level of thepresent cell, eight candidate values for the cell level CLn of thepresent cell Cn are selected according to a combination of the precedingand ensuing cell level data CLn−1 and CLn+1 as shown in FIG. 21, andideal values y0 to y7 are read from the learned table 37 (step S41), anda cell level CLn having a value closest to the actually measured value yis determined as the judged level value DL of the present cell Cn (stepS42). In FIG. 21, eight reference values for the present-cell level areextracted from the learned table 37, corresponding to a combination of(CLn−1=1) and (CLn+1=5). By performing the re-judgment as describedabove, the judged level value DL is decided as the cell level CLn, andthe cell level CLn is rewritten to the decided value DL in the RAM 31(step S43).

Successively, judging multivalued levels of the following cells by usingthe multivalued data rewritten as above can further decrease aprobability of erroneous judgment.

Besides, readings and writings from/to the RAMs 27, 30 and 31 and otheroperational processes are timed in synchronization with the samplingtiming by the sampling-synchronization detecting unit 22 shown in FIG.10.

Measuring error rates on an individual cell basis according to thepresent fourth embodiment has revealed that the error rate becomesapproximately 0.4% in a case of a cell length being 0.40 μm, which isimproved with respect to a level judgment based only on a present cell.

Next, a description will be given, with reference to FIG. 23 to FIG. 27,of a fifth embodiment according to the present invention. In theabove-described embodiments, relations between the present cell and thepreceding cell, the ensuing cell or the preceding cell and the ensuingcell are learned beforehand, and the learned table representing thelearned results is used for judging a level of a present cell; however,the present fifth embodiment provides a method for judging a level of apresent cell in which judgment processes as mentioned above areperformed with respect to a plurality of consecutive cell rows so as toselect out a plurality of correct-level candidate rows, among which acombination involving a smallest error is determined as a judged levelvalue of the present cell.

A description will be given, with reference to FIG. 23, of a concept ofthe present fifth embodiment. First, an operation begins with a knownmultivalued level as an initial value. The preceding-cell referencetable 33 is referred to according to this known initial value so as toselect three candidates (a cell level value involving a smallest errorbetween y and y1, a level value equaling the cell level value plus 1,and a level value equaling the cell level value minus 1). Similarly,with these three candidates being as known values, the preceding-cellreference table 33 is referred to according to these known values so asto select further three candidates. By the heretofore-performedoperation, combinations of nine candidates can be extracted ascombinations of a present-cell level and an ensuing-cell level.

With respect to each of these combinations of the nine candidates, a sumof squares Σ(σi0²+σij²) of errors between the learned table and observedvalues is calculated, where 1≦i, j≦3 stands (see FIG. 24). A combinationinvolving the smallest sum of squares of errors is calculated so as todetermine a judged level value of the present cell corresponding to thiscombination to be a correct level. Repeating this operation successivelycan further enhance a probability of obtaining a correct level.Additionally, although selection of candidates is performed with respectonly to combinations of a present cell and an ensuing cell in thepresent fifth embodiment, the selection of candidates may be repeatedwith respect further to a cell following the ensuing cell, as shown inFIG. 25 and FIG. 26, so as to further enhance a probability of obtaininga correct level.

In the present fifth embodiment, the table referred to according to apreceding-cell level (the preceding-cell reference table 33) is used;however, a probability of obtaining a correct judgment can be similarlyenhanced by a method of judging a level of only the present cell first,and based on a result of this judgment, switching the preceding-cellreference table 33 and the ensuing-cell reference table 35 as describedabove; alternatively, a probability of obtaining a correct judgment canbe similarly enhanced by performing the selection of candidate valuesand the calculation of errors by using thethree-successive-recording-mark learned table 37.

FIG. 27 is a flowchart showing an algorithm of extracting combinationsof candidate values for a present cell and an ensuing cell; andselecting a correct combination, by using thethree-successive-recording-mark learned table 37. Processes in steps S1to S6 and S41 shown in FIG. 27 are performed in the same manner as inthe steps S1 to S6 and S41 shown in FIG. 22. After the step S41, basedon a comparison between y and yi, candidate values X10, X20 and X30 areselected (step S51), and errors σ10, σ20 and σ30 between y and yi arecalculated (step S52). Thereafter, assuming one candidate value X10 tobe CLn, comparison reference values y0 to y7 for a present-cell levelare extracted according to a relation between CLn−1 and CLn+1 (stepS53). Then, according to a comparison between y and yi, candidate valuesX11, X12 and X13 are selected (step S54), and errors σ11, σ12 and σ13between y and yi are calculated (step S55).

Also, assuming another candidate value X20 to be CLn, comparisonreference values y0 to y7 for the present-cell level are extractedaccording to a relation between CLn−1 and CLn+1 (step S56). Then,according to a comparison between y and yi, candidate values X21, X22and X23 are selected (step S57), and errors σ21, σ22 and σ23 between yand yi are calculated (step S58). Similarly, assuming another candidatevalue X30 to be CLn, comparison reference values y0 to y7 for thepresent-cell level are extracted according to a relation between CLn−1and CLn+1 (step S59). Then, according to a comparison between y and yi,candidate values X31, X32 and X33 are selected (step S60), and errorsσ31, σ32 and σ33 between y and yi are calculated (step S61).

Based on results of these calculations, a combination path involving thesmallest sum of squares of errors is found to be correct so as todetermine the cell level CLn corresponding to this combination as ajudged level value DLn (step S62).

Besides, as a method for reducing an amount of calculation, not only thepresent cell, but also the ensuing cell of the above-mentionedcombination involving the smallest sum of squares of errors may betreated as correct. Specifically, the above-described operation may becommenced successively by treating the ensuing cell as having a knownvalue in a following process. Additionally, although the present fifthembodiment uses a combination of the three candidates “a cell levelvalue involving a smallest error between y and yi, a level valueequaling the cell level value plus 1, and a level value equaling thecell level value minus 1,” using two candidates close to y can reduce anamount of calculation. In this case, the number of combinations ofcandidates for a present cell and an ensuing cell becomes four so as toreduce an amount of calculation by more than half.

In addition, although the above-described embodiments feature a systemwith which a user can record and reproduce information, the same appliesto a ROM (Read Only Memory) disc as a recording medium used only forreproduction. For instance, the learned patterns used for creating thepresent-cell judgment table 29, the preceding-cell reference table 33and the ensuing-cell reference table 35 are formed beforehand as phasepits (pits formed on a disc substrate in an uneven form) together withROM information used by a user. Reading these learned patterns asdescribed above enables a prevention of an erroneous judgment of a levelalso in a ROM disc.

Further, in the above-described embodiments, the learned informationarea is provided on the innermost area of the recording medium 3 onwhich user data is not recorded; however, the learned information areamay be provided at a head of each block (e.g., a unit of 256 cells,i.e., a unit of 256*3 bits) in which user data is recorded. According tothis arrangement, recording/reproducing can be performed while learningso as to further decrease a probability of erroneous judgment.

Next, a description will be given, with reference to FIG. 28 to FIG. 30,of a sixth embodiment according to the present invention. The presentsixth embodiment adopts the first principle and the sixth principle ofthe present invention.

As shown in FIG. 28, an information recording/reproducing deviceaccording to the present sixth embodiment has basically the samestructure as the information recording/reproducing device shown in FIG.7, except the hereinbelow-described points. In the present sixthembodiment using the first principle and the sixth principle, uponrecording information on the information recording medium 3, whileperforming a recording with N-valued marks (N=8), an M-valued mark (M=4)with a reduced number of levels is recorded on one cell in everypredetermined number (=3) of cells, as described above with reference toFIG. 1C; by reproducing information according to the first principlefrom the information recording medium 3 on which multivalued informationis recorded as described above, an erroneous judgment with respect to amultivalued level can be prevented, and also successive erroneousreadings starting from one erroneous reading of a cell level due to adefect and so forth can be prevented.

Therefor, a multivalued-level judging unit 113 according to the presentsixth embodiment comprises an operation unit 118 judging a cell level,and a cell level retaining unit (a judged level value retaining unit)119 retaining cell level data of a preceding cell, as shown in FIG. 29.The operation unit 118 comprises a table RAM 120 storing level datacorresponding to each input digital data (each reproduction level), andan address generating unit 121 reading cell level data e from the tableRAM 120 according to a preceding cell level f and a value of the digitaldata c.

The table RAM 120 comprises a preceding-cell-based table area (addresses0-8191) storing groups of cell level data determined according to eachof cell levels of a preceding cell, and a four-valued cell table area(addresses 8192-9215) storing cell level data of four-valued cells, asshown in FIG. 30. That is, the table RAM 120 stores cell level data ataddresses corresponding to values of the digital data c, the cell leveldata being divided according to cell level data of a preceding cell. Forexample, when the cell level data of the preceding cell is “2”, and thedigital data is “131”, cell level data “1” is read from an address of“2*1024+131”. That is, by adding an offset generated from the cell leveldata of the preceding cell to the address of the digital data andreading from the address, criteria for judging the cell level can bechanged according to the preceding cell so as to generate the cell levelthereby. This 3-bit cell level data row reproduced from each cell iscollected by the cell-data converting unit 14 so as to form thereproduction information g which is an 8-bit data row. As for a cell onwhich a four-valued mark is recorded, a level thereof is judgedaccording to the four-valued cell table area. As described above, sincethe table RAM 120 separately comprises the preceding-cell-based tablearea (addresses 0-8191) and the four-valued cell table area (addresses8192-9215), numbers of multivalued judgment levels can be switchedbetween eight values and four values. Thus, multivalued levels of cellshaving different numbers of levels are judged by accessing appropriateaddresses on the table RAM 120.

A description will be given, with reference to a process transitiondiagram shown in FIG. 31 and a flowchart shown in FIG. 32, of an exampleof an information reproducing process according to the present sixthembodiment. In this example, multivalued information is recorded on theinformation recording medium 3 such that a four-valued mark is recordedon one cell in every three cells, as shown in FIG. 1C and FIG. 31,according to the method indicated in FIG. 6A with the lowest-order bitbeing fixed at 00.

First, digital data SL_(N) of an Nth cell is read (step S101 shown inFIG. 32), and cell level data CL_(N) thereof is obtained from thepreceding-cell-based table area of the table RAM 120 according to thedigital data SL_(N) and a known reproduction level CL_(N−1) of apreceding cell located at a start of an information recording (stepS102). By this process, the judged cell level of the Nth cell isretained in the cell level retaining unit 119 so as to be used forgenerating an address upon reproducing a next (N+1)st cell.Subsequently, digital data. SL_(N+1) of the (N+1) st cell is read (stepS103), and cell level data CL_(N+1) thereof is obtained from thepreceding-cell-based table area of the table RAM 120 according to thedigital data SL_(N+1) and the cell level data CL_(N) (step S104). Next,digital data SL_(N+2) of an (N+2)nd cell is read (step S105). Since this(N+2)nd cell is a cell with a four-valued mark, cell level data CL_(N+2)thereof is obtained from the four-valued cell table area of the tableRAM 120 according to the digital data SL_(N+2) alone by switching thenumber of multivalued judgment levels to four (=M) values (step S106).By this process, the judged (four-valued) cell level of the (N+2)nd cellis retained in the cell level retaining unit 119 so as to be used forgenerating an address upon reproducing a next (N+3)rd cell.

From step S107 onward, processes similar to the steps S101 to S106 arerepeated so as to obtain a multivalued level of each cell of theinformation recording medium 3 on which a four-valued mark (with thelowest-order bit being fixed at 0) is recorded on one cell in everythree cells.

The cell level data e of 3-bit cells obtained as above is converted bythe cell-data converting unit 14 into an 8-bit data row by omitting thelowest-order bit of the four-valued cell, as shown in FIG. 1D, so as toform the reproduction information g.

According to the above-described information reproducing process, evenwhen one cell is erroneously reproduced due to a defect and so forth,subsequent cells can be reproduced without causing successive errors.

Next, a description will be given, with reference to FIG. 33 to FIG. 36,of a seventh embodiment according to the present invention. The presentseventh embodiment adopts the second principle and the sixth principleof the present invention. Upon recording multivalued information on theinformation recording medium 3, an M-valued mark (M=4) with the reducednumber of levels is recorded on one cell in every two cells such that acell with an N-valued mark (N=8) and a cell with an M-valued mark (M=4)alternate (see FIG. 35); thus-recorded information is reproduced fromthe information recording medium 3 by referring to a judged level valueof an ensuing cell, whereby an erroneous detection of a multivaluedlevel can be prevented, and also successive erroneous readings startingfrom one erroneous reading of a cell level due to a defect and so forthcan be prevented.

In the present seventh embodiment, an information recording/reproducingdevice has basically the same structure as the informationrecording/reproducing device shown in FIG. 28, except that amultivalued-level judging unit 113A shown in FIG. 33 is used in place ofthe multivalued-level judging unit 113 shown in FIG. 29. Themultivalued-level judging unit 113A according to the present seventhembodiment comprises a digital data retaining unit 122, a four-valuedcell level operation unit 123 as an ensuing cell level operation unit, afour-valued cell level retaining unit 124, an eight-valued cell leveloperation unit 125, a delay unit 126, and a switching unit 127. Thedigital data retaining unit 122 retains digital data c of a precedingcell. The four-valued cell level operation unit 123 detects a cell levelof an M-valued mark (M=4). The four-valued cell level retaining unit 124retains the cell level data of a four-valued mark detected by thefour-valued cell level operation unit 123, and outputs the cell leveldata of a four-valued mark upon reproducing a next cell level. Theeight-valued cell level operation unit 125 detects a cell level of apresent cell according to a cell level of an ensuing cell ensuing thepresent cell. The delay unit 126 delays an operational timing of theeight-valued cell level operation unit 125 by a one-cell period. Theswitching unit 127 switches output controls so as to alternately outputthe cell level of a four-valued mark detected by the four-valued celllevel operation unit 123 and the cell level of an eight-valued markdetected by the eight-valued cell level operation unit 125.

Similarly to the operation unit 118 shown in FIG. 29, the four-valuedcell level operation unit 123 comprises a table RAM 128, and an addressgenerating unit 129 generating an address on the table RAM 128 accordingto digital data c so as to read a cell level of a four-valued mark fromthe table RAM 128 according to the address. The table RAM 128 comprisesonly a four-valued cell table exclusively storing cell level data of afour-valued mark, as shown in FIG. 34A.

The eight-valued cell level operation unit 125 detects a cell level of apresent cell by referring to a cell level of an ensuing cell, asmentioned above, and comprises a table RAM 130, and an addressgenerating unit 131. The table RAM 130 comprises an ensuing-cell-basedtable storing cell levels of a present cell grouped according to each ofcell levels of an ensuing cell, as shown in FIG. 34B. The addressgenerating unit 131 reads cell level data from the table RAM 130according to the digital data c.

With the above-described structure, a description will be given, withreference to a process transition diagram shown in FIG. 35 and aflowchart shown in FIG. 36, of an example of an information reproducingprocess according to the present seventh embodiment. In this example,multivalued information is recorded on the information recording medium3 such that a four-valued mark is recorded on one cell in every twocells, as shown in FIG. 35, according to the method indicated in FIG. 6Awith the lowest-order bit being fixed at 0.

First, digital data SL_(N) of an Nth cell is read as digital data of apresent cell (step S111), and the digital data SL_(N) is retained in thedigital data retaining unit 122. Successively, digital data SL_(N+1) ofan (N+1)st cell is also read (step S112). Since this (N+1)st cell is acell with a four-valued mark, four-valued cell level data CL_(N+1)thereof is read by the four-valued cell level operation unit 123referring to the table RAM 128 according to the digital data SL_(N+1)alone obtained from a reproduction signal, and the four-valued celllevel data CL_(N+1) is retained in the four-valued cell level retainingunit 124 (step S113). That is, an operation for an ensuing cell, i.e.,the (N+1)st cell, is performed first. After this operation, according tothe digital data SL_(N) of the Nth cell retained in the digital dataretaining unit 122 and the four-valued cell level data CL_(N+1) suppliedfrom the four-valued cell level operation unit 123, eight-valued celllevel data CL_(N) is read by the eight-valued cell level operation unit125 referring to the table RAM 130, and is output via the Switching unit127 (step S114). Thereafter, the switching unit 127 switches outputcontrols so as to output the four-valued cell level data CL_(N+1) of the(N+1)st cell retained in the four-valued cell level retaining unit 124(step S115). Thereby, the cell level data CL_(N) and the cell level dataCL_(N+1) are output in a correct order.

From step S116 onward, processes similar to the steps S111 to S115 arerepeated with respect to an (N+2)nd cell, an (N+3)rd cell, and so forthso as to obtain a cell level of each cell of the information recordingmedium 3 on which a four-valued mark is recorded on one cell in everytwo cells. Thus-obtained cell level data e of 3-bit cells is convertedby the cell-data converting unit 14 into an 8-bit data row by omittingthe lowest-order bit of the four-valued cell so as to form thereproduction information g.

According to the above-described information reproducing process, evenwhen one cell is erroneously reproduced due to a defect and so forth,subsequent cells can be reproduced without causing successive errors.

Next, a description will be given, with reference to FIG. 37 to FIG. 40,of an eighth embodiment according to the present invention. The presenteighth embodiment adopts the third principle and the sixth principle ofthe present invention. Upon recording multivalued information on theinformation recording medium 3, an M-valued mark (M=4) with the reducednumber of levels is recorded on one cell in every two cells such that acell with an N-valued mark (N=8) and a cell with an M-valued mark (M=4)alternate (see FIG. 39); thus-recorded information is reproduced fromthe information recording medium 3 by referring to judged level valuesof a preceding cell and an ensuing cell, whereby an erroneous detectionof a multivalued level can be prevented, and also successive erroneousreadings starting from one erroneous reading of a cell level due to adefect and so forth can be prevented.

In the present eighth embodiment, an information recording/reproducingdevice has basically the same structure as the informationrecording/reproducing device shown in FIG. 28, except that amultivalued-level judging unit 113B shown in FIG. 37 is used in place ofthe multivalued-level judging unit 113 shown in FIG. 29. Themultivalued-level judging unit 113B according to the present eighthembodiment comprises a digital data retaining unit 133, a digital dataretaining unit 134, a table RAM 135, a data RAM 136 corresponding to thecell level retaining unit 119, and a sequencer 137. The digital dataretaining unit 133 retains digital data c2 of a first preceding cell.The digital data retaining unit 134 retains digital data c1 of a secondpreceding cell preceding the first preceding cell. The table RAM 135stores cell levels to be detected in an information reproducing process.The data RAM 136 temporarily retains detected and judged cell leveldata. The sequencer 137 controls the data RAM 136 and the table RAM 135.In the present eighth embodiment, the sequencer 137 and the table RAM135 together form an operation unit 138 judging a cell level.

The table RAM 135 according to the present eighth embodiment comprises apreceding-and-ensuing-cell-based table area (addresses 0-65535) storinggroups of cell level data determined according to each of cell levels ofa preceding cell and an ensuing cell, and a four-valued cell table area(addresses 65536-66559) storing cell level data of four-valued cells, asshown in FIG. 38. That is, the table RAM 135 stores cell level data ataddresses corresponding to values of digital data c, the cell level databeing divided according to cell level data of a preceding cell and anensuing cell. For example, when the cell level data of the precedingcell is “0”, the cell level data of the ensuing cell is “2”, and thedigital data is “259”, cell level data “2” is read from an address of“2*1024+259”. As for a cell on which a four-valued mark is recorded, alevel thereof is judged according to the four-valued cell table area. Asdescribed above, since the table RAM 135 separately comprises thepreceding-and-ensuing-cell-based table area (addresses 0-65535) and thefour-valued cell table area (addresses 65536-66559), numbers ofmultivalued judgment levels can be switched between eight values andfour values. Thus, multivalued levels of cells having different numbersof levels are judged by accessing appropriate addresses on the table RAM135.

With the above-described structure, a description will be given, withreference to a process transition diagram shown in FIG. 39 and aflowchart shown in FIG. 40, of an example of an information reproducingprocess according to the present eighth embodiment. In this example,multivalued information is recorded on the information recording medium3 such that a four-valued mark is recorded on one cell in every twocells, as shown in FIG. 39, according to the method indicated in FIG. 6Awith the lowest-order bit being fixed at 0. Besides, a knownreproduction level CL_(N−1) of a preceding cell at a start of aninformation recording is stored in the data RAM 136.

First, digital data SL_(N) of an Nth cell with an eight-valued mark isread as digital data of a present cell (step S121), and the digital dataSL_(N) is retained in the digital data retaining unit 133. Successively,digital data SL_(N+1) of an (N+1)st cell is also read (step S122). Sincethis (N+1)st cell is a cell with a four-valued mark, four-valued celllevel data CL_(N+1) thereof is read by the operation unit 138 referringto the four-valued cell table area in the table RAM 135 according to thedigital data SL_(N+1) alone obtained from a reproduction signal, and thefour-valued cell level data CL_(N+1) is retained in the data RAM 136(step S123). After this operation, according to the digital data SL_(N)of the Nth cell retained in the digital data retaining unit 133 and thejudged cell level data CL_(N−1) and CL_(N+1) stored in the data RAM 136,eight-valued cell level data CL_(N) is read by the operation unit 138referring to the preceding-and-ensuing-cell-based table area of thetable RAM 135, and is output under control of the sequencer 137 (stepS124). Subsequently, under control of the sequencer 137, the four-valuedcell level data CL_(N+1) of the (N+1)st cell stored in the data RAM 136is output (step S125). Thereby, the cell level data CL_(N) and the celllevel data CL_(N+1) are output in a correct order.

From step S126 onward, processes similar to the steps S121 to S125 arerepeated with respect to an (N+2)nd cell, an (N+3)rd cell, and so forthso as to Obtain a cell level of each cell of the information recordingmedium 3 on which a four-valued mark is recorded on one cell in everytwo cells. Thus-obtained cell level data e of 3-bit cells is convertedby the cell-data converting unit 14 into an 8-bit data row by omittingthe lowest-order bit of the four-valued cell so as to form thereproduction information g.

According to the above-described information reproducing process, evenwhen one cell is erroneously reproduced due to a defect and so forth,subsequent cells can be reproduced without causing successive errors.

Next, a description will be given, with reference to FIG. 41 to FIG. 43,of a ninth embodiment according to the present invention. The presentninth embodiment adopts the first principle, the second principle andthe sixth principle of the present invention. On the informationrecording medium 3, a four-valued mark is recorded on one cell in everythree cells, as in the case described above with reference to FIG. 1C.In the present ninth embodiment, an information recording/reproducingdevice has the same structure as the information recording/reproducingdevice shown in FIG. 28, and a multivalued-level judging unit has thesame structure as the multivalued-level judging unit 113B shown in FIG.37, except that the table RAM 135 according to the present ninthembodiment comprises a preceding-cell-based table area (addresses0-8191), a four-valued cell table area (addresses 8192-9215), and anensuing-cell-based table area (addresses 9216-17407) as shown in FIG.41. That is, the table RAM 135 according to the present ninth embodimenthas an arrangement equivalent to a combination of the table RAM 120shown in FIG. 30 and the table RAM 130 shown in FIG. 34B.

With the above-described structure, a description will be given, withreference to a process transition diagram shown in FIG. 42 and aflowchart shown in FIG. 43, of an example of an information reproducingprocess according to the present ninth embodiment. In this example,multivalued information is recorded on the information recording medium3 such that a four-valued mark is recorded on one cell in every threecells, as shown in FIG. 42, according to the method indicated in FIG. 6Awith the lowest-order bit being fixed at 0. This flowchart for detectingcell levels includes a reading of cell level data of a cell with afour-valued mark from the four-valued cell table area, a reading of celllevel data of a cell with an eight-valued mark following immediatelyafter the cell with the four-valued mark from the preceding-cell-basedtable area according to the cell level data of the four-valued mark, anda reading of cell level data of a cell with an eight-valued markpreceding immediately before the cell with the four-valued mark from theensuing-cell-based table area according to the cell level data of thefour-valued mark.

First, digital data SL_(N) of an Nth cell with an eight-valued mark isread (step S131), and cell level data CL_(N) thereof is obtained fromthe preceding-cell-based table area of the table RAM 135 shown in FIG.41 according to the digital data SL_(N) and a known reproduction levelCL_(N−1) of a preceding cell located at a start of an informationrecording, and is output (step S132). Subsequently, digital dataSL_(N+1) of an (N+1)st cell with an eight-valued mark is read (stepS133), and the digital data SL_(N+1) is retained in the digital dataretaining unit 133. Successively, digital data SL_(N+2) of an (N+2)ndcell is also read (step S134). Since this (N+2)nd cell is a cell with afour-valued mark, four-valued cell level data CL_(N+2) thereof is readby the operation unit 138 referring to the four-valued cell table areaof the table RAM 135 shown in FIG. 41 according to the digital dataSL_(N+2) alone obtained from a reproduction signal, and the four-valuedcell level data. CL_(N+2) is retained in the data RAM 136 (step S135).After this operation, according to the digital data SL_(N+1) of the(N+1)st cell retained in the digital data retaining unit 133 and thejudged cell level data CL_(N+2) stored in the data RAM 136, eight-valuedcell level data CL_(N+1) is read by the operation unit 138 referring tothe ensuing-cell-based table area of the table RAM 135 shown in FIG. 41,and is output under control of the sequencer 137 (step S136).Subsequently, under control of the sequencer 137, the four-valued celllevel data CL_(N+2) of the (N+2)nd cell stored in the data RAM 136 isoutput (step S137). Thereby, the cell level data CL_(N+1) and the celllevel data CL_(N+2) are output in a correct order.

From step S138 onward, processes similar to the steps S131 to S137 arerepeated with respect to an (N+3)rd cell, an (N+4)th cell, and so forthso as to obtain a cell level of each cell of the information recordingmedium 3 on which a four-valued mark is recorded on one cell in everythree cells. Thus-obtained cell level data e of 3-bit cells is convertedby the cell-data converting unit 14 into an 8-bit data row by omittingthe lowest-order bit of the four-valued cell so as to form thereproduction information g.

According to the above-described information reproducing process, evenwhen one cell is erroneously reproduced due to a defect and so forth,subsequent cells can be reproduced without causing successive errors.

Next, a description will be given, with reference to FIG. 44 to FIG. 46,of a tenth embodiment according to the present invention. The presenttenth embodiment adopts the first principle, the second principle, thethird principle and the sixth principle of the present invention. On theinformation recording medium 3, a four-valued mark is recorded on onecell in every four cells, as shown in FIG. 45. In the present tenthembodiment, an information recording/reproducing device has the samestructure as the information recording/reproducing device shown in FIG.28, and a multivalued-level judging unit has the same structure as themultivalued-level judging unit 113B shown in FIG. 37, except that thetable RAM 135 according to the present tenth embodiment comprises apreceding-cell-based table area (addresses 0-8191), a four-valued celltable area (addresses 8192-9215), an ensuing-cell-based table area(addresses 9216-17407), and a preceding-and-ensuing-cell-based tablearea (addresses 17408-82943), as shown in FIG. 44. That is, the tableRAM 135 according to the present tenth embodiment has an arrangementequivalent to a combination of the table RAM 120 shown in FIG. 30, thetable RAM 130 shown in FIG. 34B, and the table RAM 135 shown in FIG. 38.

With the above-described structure, a description will be given, withreference to a process transition diagram shown in FIG. 45 and aflowchart shown in FIG. 46, of an example of an information reproducingprocess according to the present tenth embodiment. In this example,multivalued information is recorded on the information recording medium3 such that a four-valued mark is recorded on one cell in every fourcells, as shown in FIG. 45, according to the method indicated in FIG. 6Awith the lowest-order bit being fixed at 0. This flowchart for detectingcell levels includes a reading of cell level data of a cell with afour-valued mark from the four-valued cell table area, a reading of celllevel data of a cell with an eight-valued mark following immediatelyafter the cell with the four-valued mark from the preceding-cell-basedtable area according to the cell level data of the four-valued mark, areading of cell level data of a cell with an eight-valued mark precedingimmediately before the cell with the four-valued mark from theensuing-cell-based table area according to the cell level data of thefour-valued mark, and a reading of cell level data of a cell with aneight-valued mark two cells away from the cell with the four-valued mark(a cell not adjacent to the cell with the four-valued mark) from thepreceding-and-ensuing-cell-based table area according to both the celllevel data read from the preceding-cell-based table area and the celllevel data read from the ensuing-cell-based table area. In this example,the cell with the four-valued mark is a fourth cell (N+3) from a startof an information recording, as shown in FIG. 45.

First, digital data SL_(N) of an Nth cell with an eight-valued mark isread (step S141), and cell level data CL_(N) thereof is obtained fromthe preceding-cell-based table area of the table RAM 135 shown in FIG.44 according to the digital data SL_(N) and a known reproduction levelCL_(N−1) of a preceding cell located at the start of the informationrecording (step S142). By this process, the judged cell level of the Nthcell is stored in the data RAM 136 (step S143) so as to be used forgenerating an address upon reproducing a next (N+1)st cell.Subsequently, digital data SL_(N+1), SL_(N+2) and SL_(N+3) of the(N+1)st cell, an (N+2)nd cell and an (N+3)rd cell are read in succession(steps S144, S145, S146). The digital data SL_(N+1) is retained in thedigital data retaining unit 134, and the digital data SL_(N+2) isretained in the digital data retaining unit 133. Since the (N+3)rd cellis a cell with a four-valued mark, four-valued cell level data CL_(N+3)thereof is read by the operation unit 138 referring to the four-valuedcell table area of the table RAM 135 shown in FIG. 44 according to thedigital data SL_(N+3) alone obtained from a reproduction signal, and thefour-valued cell level data CL_(N+3) is stored in the data RAM 136 (stepS147).

After this operation, according to the digital data SL_(N+2) retained inthe digital data retaining unit 133 and the judged four-valued celllevel data CL_(N+3) stored in the data RAM 136, cell level data CL_(N+2)of the (N+2)nd cell is read by the operation unit 138 referring to theensuing-cell-based table area of the table RAM 135 shown in FIG. 44, andis stored in the data RAM 136 (step S148).

Subsequently, according to the digital data SL_(N+1) retained in thedigital data retaining unit 134 and the judged cell level data CL_(N)and CL_(N+2) stored in the data RAM 136, cell level data CL_(N+1) of the(N+1)st cell is read by the operation unit 138 referring to thepreceding-and-ensuing-cell-based table area of the table RAM 135 shownin FIG. 44, and is output (step S149). Subsequently, under control ofthe sequencer 137, the cell level data CL_(N+2) of the (N+2)nd cellstored in the data RAM 136 is output (step S150), and the cell leveldata CL_(N+3) of the (N+3)rd cell stored in the data RAM 136 is output(step S151). Thereby, the cell level data CL_(N+1), the cell level dataCL_(N+2) and the cell level data CL_(N+3) are output in a correct order.

From step S152 onward, processes similar to the steps S141 to S151 arerepeated with respect to an (N+4)th cell, an (N+5)th cell, and so forthso as to obtain a cell level of each cell of the information recordingmedium 3 on which a four-valued mark is recorded on one cell in everyfour cells. Thus-obtained cell level data e of 3-bit cells is convertedby the cell-data converting unit 14 into an 8-bit data row by omittingthe lowest-order bit of the four-valued cell so as to form thereproduction information g.

According to the above-described information reproducing process, evenwhen one cell is erroneously reproduced due to a defect and so forth,subsequent cells can be reproduced without causing successive errors.

Besides, although the above-described embodiments set forth casesinvolving the information recording medium 3 using a phase change filmas a (recording-erasable) recording material allowing informationrecorded thereon to be erased, the present invention is also applicableto a case involving an information recording medium using an informationrecording film composed of magneto-optical material. Additionally, thepresent invention is applicable, not only to a rewritable-medium systemusing the recording-erasable recording material, but also to awrite-once-medium system using an organic dye or a metal film as arecordable (non-erasable) recording material. Further, in respect of aninformation reproduction, the present invention is applicable to aread-only-medium system using a read-only recording medium on whichmultivalued information marks are formed as phase pits having multipledepths, for example.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based on Japanese priority applications No.2001-232471 filed on Jul. 31, 2001 and No. 2001-232474 filed on Jul. 31,2001, the entire contents of which are hereby incorporated by reference.

1-4. (canceled)
 5. An information reproducing method for reproducing amultivalued level from a reproduction signal of a recording medium inwhich a mark representing information of said multivalued level isrecorded on a cell using a reproducing beam that covers three marks, themethod comprising: a judging step of judging a multivalued level of apresent cell by referring to a judged multivalued level of at least oneof a preceding cell preceding said present cell and an ensuing cellensuing said present cell.
 6. The information reproducing method asclaimed in claim 5, wherein said judging step judges the multivaluedlevel of said present cell by referring to a multivalued level of saidpreceding cell.
 7. The information reproducing method as claimed inclaim 5, wherein said judging step judges the multivalued level of saidpresent cell by referring to a multivalued level of said ensuing cell.8. The information reproducing method as claimed in claim 5, whereinsaid judging step judges the multivalued level of said present cell byreferring to multivalued levels of said preceding cell and said ensuingcell. 9-61. (canceled)